Biomedical subjects

D G Dervichian

Publications and source records attributed to D G Dervichian.

17 recordsLinked to original sources

PubMed1979

Enzyme-substrate interaction in lipid monolayers. I. Experimental conditions and fundamental kinetics.

A systematic study has shown the importance of the different factors which are concerned with the action of lipase on a substrate (1,3-didecanoylglycerol). These consist of a) the process of adsorption of lipase to the surface, b) the necessity of limited stirring to reach equilibrium, and c) the persistence during the reaction process of the enzyme molecules adsorbed on the monolayer. On the basis of this preliminary investigation, a technique was established to analyze the mechanism of lipase action with defined quantities of enzyme and lipid segregated in the monolayer. Thus, the process of the reaction itself is separated from the adsorption process, and it is demonstrated that the quantity of substrate hydrolyzed per minute depends only on the quantity of initially adsorbed lipase and not on the quantity of substrate or on the surface concentration of the enzyme. An appropriate new definition of the rate is consequently adopted.

Adsorption↗

PubMed1979

Enzyme-substrate interaction in lipid monolayers. II. Binding and activity of lipase in relation to enzyme and substrate concentration and to other factors.

With the limited stirring procedure used in the present work, substrate and enzyme together form a segregated and well-defined system on the surface. The lipase molecules responsible for the lipolysis are only those that are adsorbed on the glyceride monolayer. After a study of the stirring procedure, two series of systematic experiments were done: a) the bulk concentration of the enzyme was varied with different constant surface concentrations of the substrate, and b) the surface concentration of the substrate was varied with different constant bulk concentrations of the enzyme. The influence of the surface concentration of substrate on a) the rate of lipolysis, V,; b) the enzyme activity, a,; and c) the enzyme adsorption, Ze, were each determined by a different procedure. The values obtained verify the enzymic activity equation (a = V/Ze). The roles of other factors (Ca2+ ions, and pH) which govern the adsorption of the enzyme and its specific activity were also studied in preliminary experiments.

Adsorption↗

PubMed1979

Enzyme--substrate interaction in lipid monolayers. III. A study of the variation of the surface concentration with lipolysis.

Monolayers of a diacylglycerol were submitted to the action of lipase, keeping the area constant. The variation of lipase, keeping the area constant. The variation of the surface concentration gamma of the substrate with time was derived from the recorded reduction of the surface pressure pi (the isotherm of the monolayer being previously established). The rate -d gamma/dt was determined both as a function of the surface concentration gamma of the substrate and as a function of the bulk concentration C of the enzyme in the underlying solution. The rate depends on the quantity of enzyme ze adsorbed on the monolayer and on the enzymatic specific activity alpha of these adsorbed enzyme molecules. Both ze and alpha vary with gamma. The two variations have been quantitatively dissociated. The curves of ze and of alpha as functions of gamma coincide with those previously established in the study of hydrolysis under constant surface pressure.

Adsorption↗

PubMed1974