Effect of colipase on adsorption and activity of rat pancreatic lipase on emulsified tributyrin in the presence of bile salt

The present work was undertaken to examine rat pancreatic lipase activity in relation to its ability to be adsorbed on emulsified tributyrin. This study was conducted at a supramicellar concentration of sodium taurodeoxycholate, between pH 6.0 and 8.0, and at different colipase concentrations. A pH adsorption curve was differentiated from the pH activity curve of lipase. The authors concluded that the socalled acid shift of the optimal pH for lipase action described earlier is due to the low adsorption rate of lipase on its substrate at alkaline pH rather than to a change of the pH dependence of the V(max) and K(m) of the enzyme.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Purification and kinetic properties of two soluble forms of calmodulin-dependent cyclic nucleotide phosphodiesterase from rat pancreas.

The calmodulin-dependent cyclic AMP phosphodiesterase and cyclic GMP phosphodiesterase (EC 3.1.4.17) activity of rat pancreas was purified 280-fold by affinity chromatography on calmodulin-Sepharose 4B. It then accounted for 15% of the total cytosol cyclic GMP nucleotide phosphodiesterase activity, in the presence of Ca2+, and represented a minor component of proteins specifically adsorbed by the column. This activity was resolved on a DEAE-Sephacel column into two fractions, termed PI and PII, on the basis of their order of emergence. After this step, PI and PII were purified 5650- and 3700-fold respectively. The molecular weight of PI was 175 000 and that of PII was 116 000, by polyacrylamide-gradient-gel electrophoresis. Both forms of phosphodiesterase could hydrolyse cyclic AMP and cyclic GMP, although PII displayed a higher affinity toward cyclic GMP than toward cyclic AMP. PI and PII exhibited negative homotropic kinetics in the absence of calmodulin. Upon addition of calmodulin, both enzymes displayed Michaelis-Menten kinetics and a 5-9-fold increase in maximal velocity, at physiological concentrations of cyclic GMP and cyclic AMP. When a pancreatic extract freshly purified by affinity chromatography was immediately analysed by high-performance gel-permeation chromatography on a TSK gel G3000 SW column, PII represented as much as 78% of the eluted activity. This percentage decreased to 52% when the sample was stored at 0 degrees C for 20 h before analysis, suggesting that PII, possibly predominant in vivo, was converted into the heavier PI form upon storage

Simple Automated Spectrophotometric Method for Assay of Trypsin and Chymotrypsin in Duodenal Juice

Abstract Trypsin and chymotrypsin were automatically assayed by a simple spectrophotometric method, with specific ester derivatives as substrates. Samples containing 0.25 to 2.5 enzyme units in 0.5 ml were analyzed at a rate of 40 to 60 assays per hour, each sample being incubated for 6 min. The acidity developed during esterolysis was measured, with phenol red as the acid—base indicator. The full-scale deflection of the recorder, corresponding to 0.5 absorbance at 420 nm, was obtained with a sample containing 5 U of enzyme per milliliter, incubated in Tris-HCl buffer (25 mmol/liter, pH 8.0), in the presence of phenol red (124 µmol/liter). This variation corresponded to a decrease of 0.4 pH unit.</jats:p

Chemical, immunological and biological properties of peptides like vasoactive-intestinal-peptide and peptide-histidine-isoleucinamide extracted from the venom of two lizards (Helodermahorridum and Helodermasuspectum).

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Inhibition of Na/Ca exchange by Phe-Met-Arg-Phe-NH2 (FMRFa)-related peptides in intact rat pancreatic B-cells.

Phe-Met-Arg-Phe-NH2 (FMRFa)-related peptides were recently shown to inhibit Na/Ca exchange in cardiac sarcolemmal vesicles. In the present study, we examined the effects of FMRFa-related peptides on Na/Ca exchange in intact (pancreatic B) cells. At 2.8 mM glucose, FMRFa-related peptides only weakly inhibited Na/Ca exchange although their effect was more marked under depolarizing conditions. The peptides blocked neither the Na/K-ATPase nor Ca2+ channels but slightly reduced membrane K+ permeability. Our data indicate that FMRFa-related peptides are weak and non-specific inhibitors of Na/Ca exchange in intact B cells. The data do not confirm the view that the peptides may exert some of their physiological modulatory role by inhibiting Na/Ca exchange.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe