Pore diffusion: Dependence of the effective diffusivity on the initial sorbate concentration in single and multisolute batch adsorption systems

The present work studies the intraparticle diffusivity in batch adsorption systems as a function of the initial sorbate concentration. The systems under investigation are basic dyes, namely Basic Blue 69, Basic Red 22 and Basic Yellow 21 and their binary and ternary combinations, all adsorbing onto activated carbon Filtrasorb 400. They study is based on the film-pore diffusion model and the output is a combination of the external mass transfer coefficient, k_f and the effective diffusivity, D_eff that yields congruent experimental and theoretical kinetic data. It has been found the D_eff varies with C_o in an exponential decay function. Furthermore. D_eff values undergo a general reduction in the multisolute systems compared to the single component systems. Also, the relative diffusion rates in the multisolute systems are found to change such that D_eff of the slower diffuser is enhanced and that D_eff of the faster diffuser is inhibited.     

How potassium affects the activity of the molecular chaperone Hsc70. I. Potassium is required for optimal ATPase activity

Several functions of the 70-kilodalton heat shock cognate protein (Hsc70), such as peptide binding/release and clathrin uncoating, have been shown to require potassium ions. We have examined the effect of monovalent ions on the ATPase activity of Hsc70. The steady-state ATPase activities of Hsc70 and its amino-terminal 44-kDa ATPase fragment are minimal in the absence of K+ and reach a maximum at approximately 0.1 M [K+]. Activation of the ATPase turnover correlates with the ionic radii of monovalent ions; those that are at least 0.3 A smaller (Na+ and Li+) or larger (Cs+) than K+ show negligible activation, whereas ions with radii differing only approximately 0.1 A from that of K+ (NH4+ and Rb+) activate to approximately half the turnover rate observed with K+. Single turnover experiments with Hsc70 demonstrate that ATP hydrolysis is 5-fold slower with Na+ than with K+. The equilibrium binding of ADP or ATP to Hsc70 is unperturbed when K+ is replaced with Na+. These results are consistent with a role for monovalent ions as specific cofactors in the enzymatic hydrolysis of ATP.     

Intracellular pH and the role of D-lactate dehydrogenase in the production of metabolic end products by Leuconostoc lactis.

The kinetics of lactate dehydrogenase from Leuconostoc lactis NCW1 were studied. The pH optimum for the enzyme depended on the concentration of pyruvate used in the assay and the enzyme displayed an ordered mechanism with respect to substrate binding. The Km for pyruvate and NADH and the Vmax of the enzyme decreased 20-, 30- and 6-fold respectively as the pH decreased from 8.0 to 5.0. No activators were found and none of the intermediates of the phosphoketolase pathway tested inhibited the enzyme. ATP, ADP, GTP and NAD+ were inhibitory. The intracellular volume (Vol(in)) and intracellular pH (pH(in)) decreased as the extracellular pH (pH(ex)) decreased. Co-metabolism of citrate and glucose affected the Vol(in) but did not affect the pH(in), which decreased by 0.6 units per unit change in pH(ex); at pH 7.0, the pH(in) and pH(ex) were equal. The results suggest that pH(in) may play a role in determining the production of diacetyl and acetoin at low pH by Leuconostoc.     

A deficiency in aspartate biosynthesis in Lactococcus lactis subsp. lactis C2 causes slow milk coagulation

A mutant of fast milk-coagulating (Fmc+) Lactococcus lactis subsp. lactis C2, designated L. lactis KB4, was identified. Although possessing the known components essential for utilizing casein as a nitrogen source, which include functional proteinase (PrtP) activity and oligopeptide, di- and tripeptide, and amino acid transport systems, KB4 exhibited a slow milk coagulation (Fmc-) phenotype. When the amino acid requirements of L. lactis C2 were compared with those of KB4 by use of a chemically defined medium, it was found that KB4 was unable to grow in the absence of aspartic acid. This aspartic acid requirement could also be met by aspartate-containing peptides. The addition of aspartic acid to milk restored the Fmc+ phenotype of KB4. KB4 was found to be defective in pyruvate carboxylase and thus was deficient in the ability to form oxaloacetate and hence aspartic acid from pyruvate and carbon dioxide. The results suggest that when lactococci are propagated in milk, aspartate derived from casein is unable to meet fully the nutritional demands of the lactococci, and they become dependent upon aspartate biosynthesis.     

Interaction of the second binding region of troponin I with the regulatory domain of skeletal muscle troponin C as determined by NMR spectroscopy

Two dimensional 1H,15N-heteronuclear single quantum correlation NMR was used to monitor the resonance frequency changes of the backbone amide groups belonging to the 15N-labeled regulatory domain of calcium saturated troponin C (N-TnC) upon addition of synthetic skeletal N-acetyl-troponin I 115-131-amide peptide (TnI115-131). Utilizing the change in amide chemical shifts, the dissociation constant for 1:1 binding of TnI115-131 to N-TnC in low salt and 100 mM KCl samples was determined to be 28 +/- 4 and 24 +/- 4 microM, respectively. The off rate of TnI115-131 was determined to be 300 s-1 from observed N-TnC backbone amide 1H,15N-heteronuclear single quantum correlation cross-peak line widths, which is on the order of the calcium off rates (Li, M. X., Gagné, S. M., Tsuda, S., Kay, C. M., Smillie, L. B., and Sykes, B. D. (1995) Biochemistry 34, 8330-8340), and agrees with kinetic expectations for biological regulation of muscle contraction. The TnI115-131 binding site on N-TnC was determined by mapping of chemical shift changes onto the N-TnC NMR structure and was demonstrated to be in the "hydrophobic pocket" (Gagné, S. M., Tsuda, S., Li, M. X., Smillie, L. B., and Sykes, B. D. (1995) Nat. Struct. Biol. 2, 784-789).     

Development of the cocaine relapse interview: an initial report

Although fine-grained analyses of circumstances surrounding relapses have been conducted with alcoholics, smokers and opiate users, there is comparatively little information about the relapse process in cocaine abusers. The Cocaine Relapse Interview (CRI) is a structured interview that gathers information on the onset, course and termination of cocaine relapse episodes. This article describes the development of the CRI and presents initial data on its reliability and validity. Sections of the CRI assess experiences on the day of the relapse, experiences during the week prior to the relapse, attributions for the relapse, experiences following initial use of cocaine and factors in terminating the relapse. Most of the subscales in each section of the CRI had adequate internal consistency and test-retest reliabilities. Validity studies indicated that most of the subscales that assess experiences prior to relapse differentiated relapsers from two control groups of non-relapsers, and that several subscales and individual items from the sections that assess experiences following initial use and factors in termination differentiated "lapsers" from "relapsers". Limitations of the CRI and recommendations for its use were also discussed.     

Uremic leontiasis ossea: "bighead" disease in humans? Radiologic, clinical, and pathologic features

PURPOSE: To describe the clinical, radiologic, and pathologic findings in patients with uremic leontiasis ossea (ULO). MATERIALS AND METHODS: Five patients with renal osteodystrophy developed marked hyperostosis of the facial and cranial bones. Radiologic studies included plain radiography of the skull (n = 5), computed tomography with three-dimensional reconstruction (n = 4), magnetic resonance imaging (n = 3), and fluorine-18 sodium fluoride positron emission tomography (PET) (n = 1). Specimens from bone biopsies (three patients) were examined. RESULTS: Skull and facial alterations were remarkably similar. Numerous nodules of varying attenuation and signal intensity in the widened diploic space suggested brown tumors in different stages of evolution. Biochemical data and PET findings enabled confirmation of markedly increased bone turnover. Bone specimens demonstrated severe osteitis fibrosa. After parathyroidectomy, facial changes in all patients stabilized or improved mildly. CONCLUSION: A similar entity in animals, "bighead" disease, which results from nutritional and uremic secondary hyperparathyroidism, may provide a useful animal model for ULO in humans. Mild forms of this entity may be more common than the scarcity of previous reports suggests.     

Mechanisms of histamine stimulated secretion in rabbit ileal mucosa

Histamine is present in high concentrations in the intestine and we investigated the possibility that it might have a role here in intestinal transport. When added to the basal side of rabbit ileal mucosa in vitro histamine (10(-4)M) induced a short-lived increase in electrical potential difference and short circuit current. It inhibited net chloride absorption but did not influence sodium transport. Alkali secretion, measured by a pH stat technique, was inhibited, suggesting that bicarbonate secretion was reduced. Both the electrical and ion flux responses to histamine were blocked by the H1 receptor blocker diphenhydramine, but not by the H2 receptor blocker cimetidine. The presence of specific H1 histamine receptors was further supported by shifts in the dose-response curve to histamine by four different concentrations of diphenhydramine. Calculation of a pA2 value from these "Schild' plots provided a figure of 7.85, which is similar to that for H1 receptors in other tissues. Aminoguanidine, a histaminase blocker, had no electrical effects alone but shifted the histamine dose response curve to the left. These studies indicate that histamine inhibits chloride absorption and alkali secretion, possibly by influencing a chloride/bicarbonate exchange process, through specific mucosal H1 receptors. Enhancement of histamine effects by a histaminase inhibitor suggests that histaminases are present in the intestinal mucosa and supports the possibility of a role for endogenous histamine in influencing ion transport. The observations indicate a mechanism by which absorption might be impaired in diseases in which histamine is liberated locally in the intestine.