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Biomedical subjects

R Verger

Publications and source records attributed to R Verger.

180 records · Page 10Linked to original sources
PubMed1977

Further studies of mode of action of lipolytic enzymes.

Pancreatic lipase and phospholipase A2 have been shown by the monomolecular film technique to be progressively inactivated when adsorbed at the interface of their respective substrates. This inactivation is faster for lipase than for phospholipase. It is also enhanced by low film pressures and film transfer. The use of radioactive phospholipase and lipase samples offered the possibility to measure the amount of enzyme adsorbed at a monomolecular film with a reasonable accuracy. This adsorption was found to be relatively slow under the conditions of the assays. The main conclusion drawn from these data is that the enzyme kinetics in presence of a substrate film, and probably also under bulk conditions, is controlled by an adsorption flux responsible for an initial lag period and an inactivation flux tending to decrease the reaction rate. The kinetics are linear only when both fluxes equilibrate.

Adsorption↗
PubMed1977

Effects of colipase on hydrolysis of monomolecular films by lipase.

In a system free of bile salts we measured lipase hydrolysis of 1,3-didecanoylglycerol films in the presence or absence of colipase at different surface pressures. The strong, but not absolutely specific protective effect of colipase, most visible at low surface pressure, can account for the higher enzyme activity in the presence of colipase. This can be understood by taking into account simultaneous penetration and surface inactivation fluxes. Using radioactively labeled lipase, we have shown for the first time in a bile salt-free system that the critical surface pressure above which lipase can no longer penetrate a 1,2-didodecanoylphosphatidylglycerol monlayer is around 23 dynes/cm. Colipase increased this critical surface pressure to 30 dynes/cm indicating that it enables lipase penetration between 23 and 30 dynes/cm. The transfer experiment showed that colipase acts by first penetrating the lipid film and then serving as an anchor for lipase into the film.

Colipases↗
PubMed1976

Comparative studies of lipase and phospholipase A2 acting on substrate monolayers.

The kinetic aspects of lipolysis by pancreatic lipase and phospholipase A2 from different sources have been compared using monomolecular films of short chain lipids as the substrates. Phosphatidylcholine monolayers, in contrast to phosphatidylethanolamine and phosphatidylglycerol monolayers, were resistant to hydrolysis by pancreatic lipase. The induction time, measured during pre-steady state conditions, increased abruptly for a given value of the surface pressure. This appears to be due to a degree of lipid packing above which the enzyme no longer can penetrate the lipid film. The existence of an optimum in the velocity versus surface pressure profile is the result of at least two counterbalancing factors. As the surface pressure increases, the amount of enzyme present in the interface decreases, whereas the minimal specific activity of the enzyme increases. From this study with monolayers we can conclude that activity of lipolytic enzymes used as tools for probing biological membranes will be greatly influenced by the physiochemical nature of the membrane-water interface. Thus, studies such as this one which can measure the penetrating ability of various lipolytic enzymes can be useful in deriving a better understanding of biological membrane structure.

Fatty Acids↗
PubMed1976

Application of enantiomeric 2-sn-phosphatidylcholines in interfacial enzyme kinetics of lipolysis.

Two enantiomeric 2-sn-phosphatidylcholines containing hexanoyl and dodecanoyl acyl chains have been synthesized, enabling the study of the action of phospholipase A2 (EC 3.1.1.4) at lipid-water interfaces characterized by identical physico-chemical properties. Monolayer kinetics and bulk kinetics in the presence of Triton X-100 micelles were studied but the interpretation of the results is impeded by the fact that interfacial saturation conditions cannot be reached. In contrast, the use of the substrate analog n-tetradecylphosphorylcholine allows the determination of the interfacial kinetic parameters kcat and K*m. Dodecanoic acid is released from the most susceptible isomer about 13 times more rapidly than hexanoic acid from the stereoisomer in spite of the higher K*m of the former. The results are discussed in terms of the particular active site architecture and the possible influence of the "quality of the interface" on the kinetic parameters.

Binding Sites↗
PubMedDate not supplied

Synthesis and properties of novel lipopeptides and lipid mimetics.

Lipid mimetics, synthetic molecules that resemble natural lipids either structurally or functionally, have been developed as potential medicinal substances. They have been successfully applied in the development of drug and peptide delivery systems and for the development of inhibitors or lipid metabolizing enzymes. Phospholipase A2 is considered to be involved as the rate-limiting step in the production of lipid mediators of inflammatory responses and, as such, it has been a target for drug design. A series of lipid mimetics including lipopeptides, amides and alcohols of lipidic alpha-amino acids, have been tested by bulk and monolayer assay techniques. The findings suggested the direct interaction of the tested compounds with porcine pancreatic phospholipase A2. The inactivation of the enzyme occurred in a competitive manner. The most active compound I (2-amino-N-hexadecyl-L-hexanamide) showed an apparent IC50 of 12 microM and inhibitory power Z = 13 in the monolayer assay.

Animals↗
PubMedDate not supplied

Human gastric lipase: ontogeny and variations in children.

The aim of this study was to investigate the precise origin of the acid pre-duodenal lipase during human development and to evaluate its possible changes, at the tissue level, in children with gastritis or pancreatic insufficiency. Human gastric lipase appears around the 11th week of gestation and increases slowly during pre- and postnatal development. It is localized in the fundus of the stomach without any lingual localization. Human gastric lipase reaches its adult level in the third month of life, and does not vary in relation to pancreatic insufficiency. It is only rarely impaired during gastritis.

Adolescent↗