From noxiustoxin to Shiva-3, a peptide toxic to the sporogonic development of Plasmodium berghei

This communication reviews shortly the main structural and functional characteristics of Noxiustoxin, a 39 amino acid residue peptide, maintained closely packed by three-disulfide bridges and its effects on excitable membranes. Shiva-3, a cecropin like-peptide composed of 38 amino acid residues is also briefly reviewed. Its design and synthesis was made possible by the expertise gained through the work previously performed with Noxiustoxin. One of the most prominent functional characteristics of Shiva-3 is the toxic effect upon the sporogonic development of Plasmodium berghei (responsible for a murine version of malaria). A synthetic Shiva-3 gene was constructed by recursive polymerase-chain reaction (PCR) methodology and expressed using the vector pGEX2T as a hybrid protein between the glutathione-S-transferase at the N-terminal and Shiva-3 in the C-terminal part of the hybrid. The recombinant protein kills bacteria and Plasmodium berghei. The future aim of this work is to produce a transgenic mosquito that carries the message for synthesis and excretion of Shiva-3 and similar peptides, in the midgut of mosquitoes, in an attempt to control the spreading of human malaria.     

Epithelial transport of drugs in cell culture. VIII: Effects of sodium dodecyl sulfate on cell membrane and tight junction permeability in human intestinal epithelial (Caco-2) cells

This study demonstrates how the common pharmaceutical wetting agent sodium dodecyl sulfate (SDS) increases the absorption of drugs and peptides across the human intestinal epithelium. First, an assay that could follow the reversible and irreversible time-dependent effects of SDS on the permeability of Caco-2 cell monolayers with high reproducibility was developed. SDS (0.40 mM) exposure for 20 min resulted in reversible absorption enhancement of mannitol (M(r), 182 g/mol), 1-deamino-8-D-arginine-vasopressin (M(r), 1071 g/mol), and polyethylene glycol (M(r), 4000 g/mol). A longer (2 h) exposure to SDS resulted in irreversible absorption enhancement. Second, transepithelial electrical resistance measurements (TEER) together with fluorescence and transmission electron microscopy were used to study the effects of SDS on epithelial integrity, cell membranes, intracellular calcium concentration, cytoskeleton, and tight junctions. The effect of SDS (0.40 mM) on epithelial integrity was immediate. A significant decrease in transepithelial electrical resistance measurements was obtained with 1 min after exposure to SDS that was concomitant with increases in the permeability of the apical cell membranes and intracellular calcium concentration. SDS shortened the microvilli of the cells and produced apical (but not basolateral) membrane wounds, actin disbandment, disorganization of the terminal web, and structural separation of the tight junctions. The absorption enhancement was not reduced after repair of the apical cell membranes, indicating that SDS enhances drug and peptide absorption across the intestinal epithelium by the paracellular pathway.     

Probing the basis of antibody reactivity with a panel of constrained peptide libraries displayed by filamentous phage

The structural requirements for peptide binding to an antibody may be elucidated by probing it with a variety of peptides having different constraints. To this end, we have constructed and screened a panel of peptide libraries displayed by filamentous bacteriophage. The peptides in most of the libraries have the potential for constraint by fixed Cys residues, which have been placed at different sites within a randomized amino acid sequence of varying length. When taken together, the binding data obtained from screening the panel with a given antibody allow one to determine the types of constraints that promote binding, as well as the residues that are critical for binding. We describe the construction of 11, pVIII-displayed, peptide libraries, whose sizes range from 150 million to 10 billion clones. The libraries were screened with a number of polyclonal and monoclonal antibodies against peptides, proteins and carbohydrates. Cross-reactivity with peptides was always found for antibodies produced against peptides, linear epitopes on folded proteins and, surprisingly, carbohydrates, whereas antibodies against discontinuous epitopes on proteins were found less frequently. The implications of these results are discussed in terms of the structural basis for cross-reactivity with peptides.     

Species heterogeneity of Gly-11 gramicidin A incorporated into sodium dodecyl sulfate micelles

Evidence is presented for species heterogeneity of the gly-11 analog of gramicidin A incorporated into sodium dodecyl sulfate (SDS) micelles. The evidence for species heterogeneity has been obtained using one-dimensional (1D) 1H NMR spectroscopy. The 1D spectra of the indole NH moiety of tryptophans 9, 13, and 15 show the presence of more than one species. It has been found that the heterogeneity is dependent upon the gly-11/SDS molar ratio. At high SDS concentration (i.e., gly-11/SDS of 3 mM/700 mM) the heterogeneity almost completely disappears. The temperature dependence of these 1H NMR signals suggests that the two species do not interconvert. The results of nuclear Overhauser effect spectroscopy NMR experiments indicate that one species is embedded within the micelle, while the other is nearer the aqueous interface. The importance of side chain interactions with the membrane environment in producing stable, solubilized species of small peptides in SDS micelles is illustrated.     

Identification of two distinct properties of class II major histocompatibility complex-associated peptides

We have examined the interactions of various peptides with the mouse class II major histocompatibility complex molecule I-Ak. The peptides were derived from the model protein hen egg white lysozyme (HEL). The immunodominant peptide of HEL is a 10-mer, residues 52-61. Our previous work established that this sequence contains the key residues for binding and presentation to T cells. Now we show that the binding of this 10-mer sequence resulted in complexes of I-Ak and peptide that, in SDS/PAGE (without boiling the protein), rapidly dissociated from the component alpha and beta chains. The binding interactions were studied in vitro, by incubating purified I-Ak and radiolabeled peptide, or ex vivo, by using antigen-presenting cells incubated with peptides. Peptides with additional residues at either the amino or carboxyl terminus behaved dramatically differently. Complexes of I-Ak with the longer peptides were stable to SDS/PAGE. Very few amino acid additions result in the change from unstable to stable complexes. The important issue here is that when cultured with HEL, antigen-presenting cells selected the HEL peptides containing the 52-61 sequences that favored stability [Nelson, C. A., Roof, R. W., McCourt, D. W. & Unanue, E. R. (1992) Proc. Natl., Acad. Sci. USA 89, 7380-7383]. Also, from other studies, such sequences correlate with a high immunogenicity of the peptide. We conclude that there are structural features of peptides that change the stability of the class II molecule and that are independent of the "core" peptide seen by the T cells.     

Subunit composition of delta-crystallin from embryonic chick lens. Analysis of methionine-containing tryptic peptides and cyanogen bromide peptides

The predominant protein in the embryonic chick lens, delta-crystallin, is composed of four subunits with molecular weights near 50,000. The degree to which these 4 polypeptides are the same or dissimilar was explored in delta crystallin purified from 15-day-old embryonic chick lenses by relating the numbers of methionine-containing tryptic peptides and cyanogen bromide (CNBr) peptides derived from the native protein to the average number of methionine residues per subunit. Amino acid analyses indicated that 1 mol of native delta-crystallin contains approximately 32 methionine residues, leading to an average of 8 methionine residues per subunit. Approximately equal amounts of 8 methionine-containing tryptic peptides were resolved by two-dimensional thin layer separation on cellulose sheets and by isoelectric focusing in polyacrylamide gels. Nine CNBr peptides were resolved by a combination of electrophoresis in sodium dodecyl sulfate (SDS)-polyacrylamide gels and chromatography on SDS-hydroxylapatite columns. The additive molecular weight of the 9 CNBr peptides was very close to the delta-crystallin subunit molecular weight of 50,000. Thus, the subunits of 15-day-old embryonic chick delta-crystallin have similar sequence of encoded amino acids.     

Self-assembly of designed antimicrobial peptides in solution and micelles

Hydrophobic interactions are responsible for stabilizing leucine zippers in peptides containing heptad repeats. The effects of substituting leucine by phenylalanine and alanine by glycine on the self-assembly of coiled-coils were examined in minimalist antimicrobial peptides designed to form amphipathic alpha-helices. The secondary structure of these peptides was monitored in solution and in diphosphocholine (DPC) micelles using circular dichroism spectroscopy. The leucine peptides (KLAKLAK)3 and (KLAKKLA)n (n = 3, 4) become alpha-helical with increasing concentrations of salt, peptide, and DPC. The aggregation state and equilibrium constant for self-association of the peptides were measured by sedimentation equilibrium. The glycine peptide (KLGKKLG)3 does not self-associate. The leucine peptides and phenylalanine peptides (KFAKFAK)3 and (KFAKKFA)n (n = 3, 4) are in a monomer-tetramer equilibrium in solution, with the phenylalanine zippers being 2-4 kcal/mol less stable than the equivalent leucine zippers. Thermodynamic parameters for the association reaction were calculated from the temperature dependence of the association constants. Leucine zipper formation has DeltaCp = 0, whereas phenylalanine zipper formation has a small negative DeltaCp, presumably due to the removal of the larger surface area of phenylalanine from water. Self-association of the peptides is coupled to formation of a hydrophobic core as detected using 1-anilino-naphthalene-8-sulfonate fluorescence. Carboxyfluorescein-labeled peptides were used to determine the aggregation state of (KLAKKLA)3 and (KLGKKLG)3 in DPC micelles. (KLAKKLA)3 forms dimers, and (KLGKKLG)3 is a monomer. Aggregation appears to correlate with the cytotoxicity of these peptides.     

Competitive Substrate Biodegradation during Surfactant-Enhanced Remediation

The impact of synthetic surfactants on the aqueous phase biodegradation of benzene, toluene, and p-xylene (BTpX) was studied using two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), and two nonionic surfactants, POE(20) sorbitan monooleate (T-maz-80) and octylphenolpoly(ethyleneoxy) ethanol (CA-620). Batch biodegradation experiments were performed to evaluate surfactant biodegradability using two different microbial cultures. Of the four surfactants used in this study, SDS and T-maz-80 were readily degraded by a microbial consortium obtained from an activated sludge treatment system, whereas only SDS was degraded by a microbial culture that was acclimated to BTpX. Biodegradation kinetic parameters associated with SDS and T-maz-80 degradation by the activated sludge consortium were estimated using respirometric data in conjunction with a nonlinear parameter estimation technique as μmax = 0.93 h?1, Ks = 96.18 mg∕L and μmax = 0.41 h?1, Ks = 31.92 mg∕L, respectively. When both BTpX and surfactant were present in the reactor along with BTpX-acclimated microorganisms, two distinct biodegradation patterns were seen. SDS was preferentially utilized inhibiting hydrocarbon biodegradation, whereas the other three surfactants had no impact on BTpX biodegradation. None of the four surfactants were toxic to the microbial cultures used in this study. Readily biodegradable surfactants are not very effective for subsurface remediation applications as they are rapidly consumed, and also because of their potential inhibitory effects on intrinsic hydrocarbon biodegradation. This greatly increases treatment costs as surfactant recovery and reuse are adversely affected.     

Sodium dodecyl sulphate removal from tryptic digest samples for on-line capillary liquid chromatography/electrospray mass spectrometry

An on-line microcolumn switching method was developed for the removal of sodium dodecyl sulphate (SDS) from tryptic digest samples. The system includes two micro-precolumns: a specific ionic detergent trapping column and a preconcentration column. Characterization of the proteinaceous samples, after isolation from the SDS, was performed by capillary liquid chromatography (LC) with UV absorption detection and electrospay mass spectrometry (ESI-MS). Loading and clean-up of the samples and regeneration of the detergent trapping column were performed at 50 microl min(-1), resulting in sample clean-up times of only 30 s. SDS-containing tryptic digested protein samples were directly applied to the micro-precolumns without any previous sample pretreatment. The developed microcolumn switching method permits the on-line analysis of small tryptic digest samples by capillary LC/ESI-MS in the presence of SDS. The method is completely automated and can be performed unattended. The maximum amount of SDS, in terms of loadability and breakthrough, were determined. Also studied were the selection of the loading and clean-up solvents and the recovery of the peptides. Chromatographic separations and mass spectral data confirmed the removal of SDS.     

Constraints have different concurrent effects and aftereffects on variability.

Three experiments showed that constraints imposed early in learning have different effects on variability when they are in effect and after they are removed. Task constraints, which determine how something can be done, limited the number of possible responses in a computer game. Variability constraints, which specify how differently something must be done, required that each response differ from some number of prior responses. Less restrictive constraints (Experiments 1 and 2) produced higher variability during the constraints. More restrictive constraints (Experiments 2 and 3) led to higher variability after the constraints were relaxed. The authors discuss how these differences reflect strategies acquired during the constraints (default rules) and modified in closely related ways (exception rules) afterward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal and spatial expression of the E5a protein during the differentiation-dependent life cycle of human papillomavirus type 31b

Nalpha-for-Nle-Leu-Phe-Nle-Tyr-Lys, a chemotactic peptide that binds with high affinity to the chemoattractant receptor on granulocytes and monocytes, was labeled with 99mTc using the diaminedithiol (DADT) chelating system to coordinate the Tc. 99mTc labeling of the DADT-coupled peptide was accomplished in 84% overall yield (room temperature for 10 min) using [99mTc]glucoheptonate as the donor of prereduced Tc. HPLC analysis showed two major 99mTc-labeled peptide peaks, 99mTc-DADT-Pep-I and 99mTc-DADT-Pep-II, were obtained in a ratio of 1:0.85. Using an iodoacetamide-derivatized gel to remove unlabeled peptide from the 99mTc labeling mixtures, essentially no-carrier-added (nca) high-specific activity 99mTc-labeled chemotactic peptides were obtained. The 99Tc analogues of the peptides were synthesized (72% yield) in a similar fashion and correlated with 99mTc complexes I and II by HPLC. In vitro competitive receptor binding assays of the isolated 99Tc analogues were performed against the tritiated chemotactic peptide [3H]N-for-Met-Leu-Phe ([3H]fMLF) using isolated granulocytes. The 99Tc-derivatized peptides showed similar binding affinities to the chemoattractant receptor as the unlabeled Nalpha-for-Nle-Leu-Phe-Nle-Tyr-Lys. The nca 99mTc-labeled peptides gave high contrast images of experimental inflammation in rabbits without causing neutropenia. Thus, it is feasible to attach the Tc-DADT chelate to low-molecular weight receptor binding chemotactic peptides and retain substantial binding to the receptor. Chemotactic peptides labeled with 99mTc via the DADT ligand system have the potential for imaging focal sites of inflammation without toxic effects, an important consideration in the successful utilization of chemotactic peptide agonists.     

Variable cross-resistance to Cry11B from Bacillus thuringiensis subsp. jegathesan in Culex quinquefasciatus (Diptera: Culicidae) resistant to single or multiple toxins of Bacillus thuringiensis subsp. israelensis

A novel mosquitocidal bacterium, Bacillus thuringiensis subsp. jegathesan, and one of its toxins, Cry11B, in a recombinant B. thuringiensis strain were evaluated for cross-resistance with strains of the mosquito Culex quinquefasciatus that are resistant to single and multiple toxins of Bacillus thuringiensis subsp. israelensis. The levels of cross-resistance (resistance ratios [RR]) at concentrations which caused 95% mortality (LC95) between B. thuringiensis subsp. jegathesan and the different B. thuringiensis subsp. israelensis-resistant mosquito strains were low, ranging from 2.3 to 5.1. However, the levels of cross-resistance to Cry11B were much higher and were directly related to the complexity of the B. thuringiensis subsp. israelensis Cry toxin mixtures used to select the resistant mosquito strains. The LC95 RR obtained with the mosquito strains were as follows: 53.1 against Cq4D, which was resistant to Cry11A; 80.7 against Cq4AB, which was resistant to Cry4A plus Cry4B; and 347 against Cq4ABD, which was resistant to Cry4A plus Cry4B plus Cry11A. Combining Cyt1A with Cry11B at a 1:3 ratio had little effect on suppressing Cry11A resistance in Cq4D but resulted in synergism factors of 4.8 and 11.2 against strains Cq4AB and Cq4ABD, respectively; this procedure eliminated cross-resistance in the former mosquito strain and reduced it markedly in the latter strain. The high levels of activity of B. thuringiensis subsp. jegathesan and B. thuringiensis subsp. israelensis, both of which contain a complex mixture of Cry and Cyt proteins, against Cry4- and Cry11-resistant mosquitoes suggest that novel bacterial strains with multiple Cry and Cyt proteins may be useful in managing resistance to bacterial insecticides in mosquito populations.     

A multivariate analysis of the effects of the Self-Directed Search on high school girls.

Attempted to learn how the Self-Directed Search (SDS) achieves its effects: Are the effects of the SDS on students due largely to its transparent structure and the large number of occupational options presented? Can these effects be enhanced if students are given an instructional booklet about the SDS and J. L. Holland's typology? These hypotheses were investigated in a Structure?×?Options?×?Instruction design with 104 high school girls randomly assigned to the 8 conditions. Ss were assessed before and 2 mo after treatment for their vocational aspirations, knowledge of the typology, and information seeking. The nonsignificant findings imply that the SDS achieves its effects partly because of its numerous occupational options and that the use of an instructional booklet may also increase the number of options. Some speculations about the influence of counselors and interest inventories are offered. (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibition of neuronal high voltage-activated calcium channels by insect peptides: a comparison with the actions of omega-conotoxin GVIA

The whole cell variant of the patch clamp technique was used to investigate the actions of two novel insect peptides on high voltage-activated Ca2+ currents in cultured dorsal root ganglion (DRG) neurones. The insect peptides (PMP-D2 and PMP-C) were isolated originally from insect brains and fat bodies, and have been found to have similar three-dimensional structures to the N-type Ca2+ channel inhibitor omega-conotoxin GVIA (omega-CgTx GVIA). High voltage-activated Ca2+ currents were activated from a holding potential of -90 mV by depolarizing step commands to 0 mV. Extracellular application of synthetic PMP-D2 or PMP-C (1 microM) attenuated high voltage-activated Ca2+ currents. The effects of PMP-C were strongly dependent on the frequency of current activation, but inhibition was apparent and reached a steady state after 20 steps when currents were evoked for 30 msec at 0.1 Hz. The actions of the two insect peptides overlapped both with each other and with omega-CgTx GVIA, suggesting that N-type Ca2+ current was predominantly sensitive to these peptides. Low voltage-activated T-type current and 1,4-dihydropyridine sensitive L-type Ca2+ currents were insensitive to 1 microM PMP-D2 and PMP-C, which indicates a degree of selectivity. The presence of a fucose group on PMP-C abolished the ability of this peptide to attenuate high voltage-activated Ca2+ currents, which may reflect a mechanism by which peptide function could be regulated in insects. The electrophysiological data are supported by studies on 45Ca2+ influx into rat cerebrocortical synaptosomes. Both PMP-D2 (10 microM), PMP-C (10 microM) and omega-CgTx GVIA (1 microM) attenuated a proportion of 45Ca2+ influx into the synaptosomes, but additive effects of these peptides were not observed. We conclude that these naturally occurring peptides obtained from invertebrate preparations have inhibitory effects on N-type Ca2+ channels. Although the peptides have related three-dimensional structures, they have distinct amino acid sequences and appear to have different mechanisms of action to produce inhibition of mammalian neuronal high voltage-activated Ca2+ channels.     

Membrane-induced secondary structures of neuropeptides: a comparison of the solution conformations adopted by agonists and antagonists of the mammalian tachykinin NK1 receptor

We present what we believe to be the first documented example of an inducement of distinctly different secondary structure types onto agonists and antagonists selective for the same G-coupled protein receptor using the same membrane-model matrix wherein the induced structures are consistent with those suggested to be biologically active by extensive analogue studies and conventional binding assays. 1H NMR chemical shift assignments for the mammalian NK1 receptor-selective agonists alpha-neurokinin (NKA) and beta-neurokinin (NKB) as well as the mammalian NK1 receptor-selective antagonists [d-Pro2,d-Phe7,d-Trp9]SP and [d-Arg1, d-Pro2,d-Phe7,d-His9]SP have been determined at 600 MHz in sodium dodecyl sulfate (SDS) micelles. The SDS micelle system simulates the membrane-interface environment the peptide experiences when in the proximity of the membrane-embedded receptor, allowing for conformational studies that are a rough approximation of in vivo conditions. Two-dimensional NMR techniques were used to assign proton resonances, and interproton distances were estimated from the observed nuclear Overhauser effects (NOEs). The experimental distances were used as constraints in a molecular dynamics and simulated annealing protocol using the modeling package DISCOVER to generate three-dimensional structures of the two agonists and two antagonists when present in a membrane-model environment to determine possible prebinding ligand conformations. It was determined that (1) NKA is helical from residues 6 to 9, with an extended N-terminus; (2) NKB is helical from residues 4 to 10, with an extended N-terminus; (3) [d-Pro2,d-Phe7,d-Trp9]SP has poorly defined helical properties in the midregion and a beta-turn structure in the C-terminus (residues 6-9); and (4) [d-Arg1,d-Pro2, d-Phe7,d-His9]SP has a helical structure in the midregion (residues 4-6) and a well-defined beta-turn structure in the C-terminus (residues 6-10). Attempts have been made to correlate the observed conformational differences between the agonists and antagonists to their binding potencies and biological activity.     

Effects of experimenter absence and subject briefing on social desirability scale scores.

Investigated the effects of 2 methodological variables, briefing-debriefing and E presence-absence on Ss' test-taking performance. 200 college males were randomly assigned to 1 of the 4 conditions and administered the Marlowe-Crowne Social Desirability Scale (SDS). Those Ss tested under the E-absent condition obtained a significantly lower SDS score than those in the E-present condition (p     

Ordinal position, approval motivation, and interpersonal attraction.

Attempted to incorporate ordinal position effects within approval-dependency theory. 257 undergraduates completed the Marlowe-Crowne Social Desirability Scale (SDS) and birth-order data prior to the actual experiment. Bogus SDSs were completed by the E to correspond to the same score level of the individual Ss but with either 75 or 50% item agreement. The 3 * 2 analyses of variance for SDS scores and expressed attraction indicate that 1st- and middle-born females had higher SDS scores and expressed more attraction. A separate analysis indicates that although only-born females had similar SDS scores, they expressed significantly more attraction. Correlations between SDS scores and expressed attraction were significant. Results are interpreted as being congruent with approval-dependency theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Risk of uterine leiomyomata among premenopausal women in relation to body size and cigarette smoking

Growth acceleration and bone maturation were studied for 3 y in 69 children with severe short stature and a history of intrauterine growth retardation (IUGR), to determine the effect of treatment with recombinant human growth hormone (r-hGH). The patients were enrolled in an open, multicentre trial and were randomly allocated to either the treated group (Group 1) or the control group (Group 2). The children in Group 1 were treated daily with 0.2 IU/kg/body weight (0.067 mg/kg) s.c., during 3 y and the children in Group 2 started the study with a 1-y observation period followed by a 3-y treatment period. At birth, their mean weight standard deviation score (SDS) was -2.5 and their mean length SDS -3.5. At baseline, the patients were prepubertal, non-GH deficient, with no known dysmorphic features. Mean age was 4.5 y, bone age was 3.3 y, height SDS was -3.4, height velocity (HV) SDS was -1.6, and body mass index SDS was -1.4. After 1 y of treatment, linear HV in Group 1 increased in comparison with the pre-treatment period (from 5.7 +/- 2.0 to 10.1 +/- 1.7 cm/y; p < 0.001) and with the first year of observation in Group 2 (p < 0.001). Increased HV was sustained during the second and third year of treatment and was significantly higher than at baseline. A similar growth pattern was seen during the 3 y of GH treatment in Group 2. Mean height SDS for chronological age increased by 2.0 +/- 0.7 in the two groups after 3 y of treatment. HV after 1 y of treatment was negatively correlated with growth velocity at baseline. Bone age remained retarded but increased with a mean of almost 4 y after 3 y of treatment in both groups. Even at a dose that is three times the replacement dose treatment with r-hGH was well tolerated. From these results, we conclude that r-hGH treatment over 3 y can induce sustained catch-up growth in young children with severe short stature and a history of IUGR. Long-term studies are needed to assess ultimate effects on final height.     

Identification of a steroidogenic neurohormone in female mosquitoes

In the female mosquito, Aedes aegypti, neurohormones are released from the brain in response to a blood meal and stimulate the ovaries to secrete ecdysteroid hormones, which modulate yolk protein synthesis in the fat body. Neuropeptides with this bioactivity were isolated from head extracts, and partial sequences from these peptides when aligned gave a 31-residue sequence at the amino terminus. Oligonucleotide primers for this sequence were used to amplify with the polymerase chain reaction a genomic DNA product that hybridized to a clone from a head cDNA library. The cDNA encodes a 149-residue preprohormone that is processed into an 86-residue peptide, as indicated by the mass value obtained from the native peptide, with the expected amino-terminal sequence. After modification, the cDNA for the putative neurohormone was expressed in a bacterial system, and the purified peptide had high specific activity in bioassays, thus confirming that it is a steroidogenic gonadotropin, the first to be identified for invertebrates.     

Calcitonin secretion in vitro. III. Synergistic secretory effects of enteric polypeptide hormones

Crude and highly purified preparations of enteric peptide hormones were shown to stimulate trout calcitonin (tCT) secretion in vitro. Since the maximal stimulatory effects of crude pancreozymin/secretin preparations were seen to be greater than the secretory effects obtained with the individual purified enteric peptides, the current study has focused on the secretory effects of several combinations of enteric peptides. The additive and synergistic secretory effects of various specific peptide combinations are demonstrated. Marked (85-fold) stimulation tCT secretion occurs in response to combinations of synthetic secretin (5 X 10(-5)M) with pentagastrin (10(-6)M) or the carboxylterminal octapeptide of pancreozymin (10(-6)M). These findings have significance with regard to the potentiation of hormone action, and are preliminary evidence for the presence of separate receptors for various enteric peptide secretagogues on C-cells.