Nucleotide receptors in the nervous system. An abundant component using diverse transduction mechanisms

Extracellular nucleotides achieve their role as cell-to-cell communicators by acting at cell surface transmembrane receptors-the P2 receptors. Before molecular cloning led to the isolation of any P2-receptor sequence, a small number of receptor types had been proposed on the basis of pharmacological evidence. The application of molecular biology to this field of receptor research has indicated that a great underestimation of the number of receptor subtypes and of their abundance had occurred. There are now known to be seven characterized P2Y (G protein linked) receptors and the same number again of P2X receptors of the transmitter-gated ion channel type. In this review, we discuss the properties of these cloned receptors, their distribution within the nervous system, and their methods of signal transduction.     

Nucleotide excision repair of melphalan monoadducts

The nucleotide-excision repair (NER) system removes bulky DNA adducts and is thought to be involved in resistance to chemotherapeutic drugs, which act by damaging DNA. In this study, we have investigated the ability of the NER system to recognize and excise melphalan monoadducts from a 140-mer DNA substrate. We show that rodent and human cell-free extracts (CFEs) excise 26-29-nt-long oligomers from a synthetic 140-mer containing centrally located melphalan adducts. CFEs from cell lines with mutations in xeroderma pigmentosum group F or G genes did not excise these alkylated oligomers; however, mixing the two CFEs restored excision activity to the level found with wild-type CFEs. These results demonstrate the ability of the NER system to excise melphalan monoadducts, and are consistent with the hypothesis that NER may be involved in resistance to melphalan chemotherapy.     

Nucleotide specificity of human deoxycytidine kinase

The ability of deoxycytidine kinase (dCK) to phosphorylate 2'-deoxycytidine (dCyd) and its analogs in the presence of eight nucleoside triphosphates (NTPs), simulating the cellular milieu, was investigated. Using highly purified dCK from MOLT-4 T lymphoblasts, Km and Vmax values were determined for the phosphorylation of dCyd in the presence of cellular concentrations of the eight endogenous NTPs. The results demonstrated that the efficiency of dCyd phosphorylation was greatest in the presence of all eight nucleotides, relative to ATP alone, according to relative Vmax/Km values. UTP was a better phosphate donor than ATP but was less efficient than the NTP mixture. The greater efficacy of the NTP mixture, compared with ATP alone, was due in large part to the presence of UTP, although the results suggested that the presence of other nucleotide(s) also enhanced dCyd phosphorylation. Previous results demonstrated that dCTP was a potent competitive or noncompetitive (with respect to dCyd) inhibitor of dCK, with a Ki value of approximately 1 microM. In contrast, the results presented here demonstrated that, in the presence of either the NTP mixture or UTP, inhibition of dCK was uncompetitive with respect to dCyd, with a Ki value of approximately 60 microM. Furthermore, the results demonstrated that the clinically relevant nucleoside analogs 1-beta-D-arabinofuranosylcytosine, 2',2'-difluoro-2'-deoxycytidine (dFdC), and 9-beta-D-arabinofuranosyl-2-fluoroadenine also preferred UTP or the NTP mixture, compared with ATP alone, as a phosphate donor. Of the three nucleoside analogs tested, dFdC was the most efficient dCK substrate. These data indicate that the preferred phosphate donor for dCK is UTP or a combination of UTP and another nucleotide. Furthermore, the dCTP concentration in intact cells, which is typically 10-20 microM, is not sufficient to cause substantial inhibition of dCK, due to the presence of UTP. Strategies to increase cellular dCK activity should focus on optimizing UTP concentrations.     

Nucleotide sequence of cucurbit aphid-borne yellows luteovirus

The nucleotide sequence (5669 residues) of the genomic RNA of cucurbit aphid-borne yellows luteovirus (CABYV) is presented. Analysis of genome organization and sequence homologies indicate that CABYV is a member of luteovirus Subgroup 2 (other sequenced members: beet western yellows virus, potato leafroll virus, and barley yellow dwarf virus, RPV isolate) and appears to be most closely related to beet western yellows virus.     

Nucleotide sequence of bacteriophage G4 DNA

The 5,577 nucleotide long sequence of bacteriophage G4 DNA has been determined using the 'plus and minus' and chain termination methods of DNA sequencing. This sequence has been compared with that of the closely related bacteriophage phiX174 (refs 1, 55). In the coding regions there is an average of 33.1% nucleotide sequence differences between the two genomes, but the distribution of these changes is not random and the sequence of some genes is more conserved than others. There is less sequence similarity between the untranslated intergenic regions of G4 and phiX174, but despite this the sequences of the J/F, F/G and H/A untranslated spaces in both genomes have similar sized hairpin loops, which may be related to their function.     

Nucleotide inhibitors and activators of retinal guanylyl cyclase

The restoration of the dark state in retinal rod cells following illumination is due in part to resynthesis of cGMP. Retinal guanylyl cyclase specifically catalyzes the cyclization of GTP into cGMP in vivo. The reaction has been shown to involve the inversion of the configuration on the phosphate atom as demonstrated by conversion of the (SP) isomer of GTP alpha S to (RP)-cGMPS by guanylyl cyclase [Senter, P. D., Eckstein, F., Mülsch, A., & B?hme, E. (1983) J. Biol. Chem. 258, 6741-6745]. Since (RP-cGMPS is not a substrate for retinal phosphodiesterase, we were able to measure cyclase activity with greater reliability using this novel assay as opposed to other published procedures. This assay has allowed us to reinvestigate the effects of adenylyl nucleotides on cyclase activity and to search for selective inhibitors of the rod-specific enzyme. We have measured the cyclase activity using homogenates of rod outer segments and a reconstituted system composed of guanylyl cyclase in washed rod outer segment membranes and the purified guanylyl cyclase activating protein. Our results indicate that 100-200 microM ATP (and other adenylyl nucleotides) stimulates guanylyl cyclase activity approximately 2-fold and that the observed stimulation of enzyme activity is independent of the free calcium concentration. In contrast to other particulate guanylyl cyclases, which are synergistically stimulated by a peptide ligand and ATP, guanylyl cyclase activating protein does not potentiate the effect of ATP, suggesting that retinal guanylyl cyclase may be regulated differently. ATP changes the Vmax of retinal guanylyl cyclase without changing the Km for (SP)-GTP alpha S.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinin receptors

The theory that obsessions are caused by catastrophic misinterpretations of one's intrusive thoughts/ images/impulses is elaborated in an attempt to explain the frequency of obsessions and why they persist. The internal and external provocations of obsessions are considered, and an explanatory framework for the varying contents of obsessions is set out. The role and functions of neutralization and inflated responsibility are assessed, and the treatment implications of the theory are described.     

Purinergic receptors

The aim of the present paper was characterization of purinergic receptors specific for nucleotides (P2) and nucleosides (P1). Their subclassification, distribution and functions have been briefly described.     

Leukotriene receptors

The current challenge in research on leukotriene receptors is to clone these molecules. Traditional protein purification approaches have not been successful in providing sequence information. Solubilization of cys-LT1 has been achieved but results in the dissociation of G-proteins and the loss of high affinity binding (Mong et al., 1986b; Mong and Sarau, 1990), while cys-LT2 activity cannot be monitored by other than functional assays and there have not been any purification attempts. Partial purification of B-LT has been reported but has not been continued to homogeneity (Sherman et al., 1992; Votta et al., 1990; Miki et al., 1990). Nor have attempts to clone these receptors through either homology screening or expression cloning been successful. The cloning of the prostanoid receptors, described in detail elsewhere in this volume, has shown that these receptors belong to a distinct family within the G-protein-coupled receptor superfamily. It is probable, therefore, that the leukotriene receptors will also belong to a separate group within this superfamily since phylogenic comparisons have shown that receptors displaying high affinity for structurally related ligands exist as discrete families. Recently, a human cDNA encoding an orphan FMLP-related receptor cloned from HL60 cells of myeloid lineage was identified as the receptor for another eicosanoid, lipoxin A (Fiore et al., 1994). FMLP has a similar profile of biological actions to LTB4. Moreover, LTD4 showed a high degree of cross-reactivity with this receptor with an affinity only 20-fold less that of lipoxin A, although LTB4 was inactive. It remains to be determined whether the leukotriene receptors will fall into this class of receptors. The cloning of the leukotriene receptors will allow identification of the different receptor types and subtypes and potentially splice variants. Evaluation of currently developed antagonists at these receptor types could also open the way for novel therapies for inflammatory conditions.     

Nucleotide substitution in the bovine FSHB 5''-region

We monitored the electrocardiogram of 20 fathers while their child was born. Paternal heart rate rose on average by 53% during delivery from the starting point frequency (72 beats/min.) to the maximum (115 beats/min.) just before the birth of the child. Judging from the heart rate variation, paternal sympathetic activity increased by 25% and vagal tone decreased by 22% during delivery. No derangements in cardiac function were encountered, not even in the man who fainted.     

Nucleotide sequence of the human tyrosine aminotransferase gene

Introns of human tyrosine aminotransferase (TAT) gene were sequenced. Combined with the literature data about the exon-intron structure of the gene and the sequence of the TAT mRNA, the obtained nucleotide sequences yielded on uninterrupted segment 10989 b. p. long of the human TAT gene.     

Nucleotide sequence of alkyl-dihydroxyacetonephosphate synthase cDNA from Dictyostelium discoideum

OBJECTIVE AND IMPORTANCE: Congenital anomalies of the posterior arch of the atlas (C1) are uncommon. They range from partial clefts to total agenesis of the posterior arch. Developmental cervical canal stenosis is a congenital anomaly that may cause cervical myelopathy. Myelopathy caused by cervical stenosis at the level of the atlas has been reported in only three cases. We present two cases of nontraumatic cervical myelopathy caused by spinal stenosis at the level of the atlas associated with a hypoplastic but complete posterior arch of C1. CLINICAL PRESENTATION: Two elderly Chinese men developed cervical myelopathy gradually during months to years, without preceding trauma. Imaging revealed a hypoplastic but complete posterior C1 arch associated with changes of spondylosis in both patients, producing severe spinal stenosis and spinal cord compression. Posterior decompression was achieved in both by the removal of the posterior arch of C1 with its surrounding thickened posterior ligaments. Symptoms and clinical findings improved in the two patients during the follow-up period. CONCLUSION: The anomaly presented in our two cases differs from the established classification of congenital abnormalities of the posterior arch of the atlas, suggesting a different embryological defect. The hypoplastic posterior C1 arch created a congenitally narrowed spinal canal in our patients, rendering the spinal cord more susceptible to compression related to degenerative changes of the spine. Surgical removal of the shortened posterior C1 arch and surrounding degenerative ligaments is an effective treatment for symptomatic patients with this condition.     

Nucleotide sequence and genome structure of mink enteritis virus

Diabetes mellitus is a common disease. It affects multiple organ systems. Adverse effects of hyperglycemia on infection, fracture healing, and bone remodeling have been recently reported. This study was conducted to evaluate the clinical and radiographic results of 93 total hip arthroplasties in 78 consecutive patients with diabetes. All femoral components were cemented using contemporary cementing techniques. Prophylactic antibiotics were given in each case. The mean follow-up period was 4.1 years (range, 2-6.5 years). Ninety-six percent of the hips were rated excellent or good. Radiolucencies were observed in only 3.7% of the stems, while 22.2% of the cups showed radiolucencies. There was a 4% revision incidence. There was no postoperative infection in this series--a distinct improvement from previously reported series. However, complications remained high at 24.3%. The most frequent complication was urinary tract infection (14.2%). The most serious complication was myocardial infarction. The authors believe total hip arthroplasty can be safely performed in patients with diabetes, provided that adequate medical and follow-up evaluations are performed. The medium-term clinical and radiographic follow-up evaluations are not inferior to reported series in patients without diabetes.     

Nucleotide sequence of ToxPK1 gene from Toxoplasma gondii

We report here for the first time a complete nucleotide sequence (6.8 kb) of a protein kinase gene (ToxPK1) from the obligate intracellular protozoan parasite of man, Toxoplasma gondii. This gene comprising putatively of 9 exons and 8 introns forms the Toxoplasma gene with the largest number and size of introns reported so far. The predicted protein with 508 amino acids contains the 15 invariant residues as well as the characteristic motifs specific to protein serine/threonine kinases. Homology-based computational comparisons suggested that TOXPK1 belongs to or closely resembles the SNF1 subfamily of protein-serine/threonine kinases. Based on the functions of SNF1 homologs in other organisms and our RT-PCR results, it is likely that TOXPK1 may be transiently expressed to up-regulate glycogen biosynthesis during the development of tachyzoites into bradyzoites.