Christian Gancet

Competitive inhibition of lipolytic enzymes. I. A kinetic model applicable to water-insoluble competitive inhibitors.

It is now becoming clear from the abundant lipolytic enzyme literature that any meaningful interpretation of inhibition data has to take into account the kinetics of enzyme action at the lipid/water interface. We attempt in the present paper to provide a kinetic model applicable to water-insoluble competitive inhibitors, in order to quantitatively compare the results obtained at several laboratories. We derived kinetic equations applicable to the pre-steady state as well as steady state. By measuring the inhibitory power, as described in the present paper, it is possible to obtain a normalized estimation of the relative efficiency of various potential inhibitors. Furthermore, with the kinetic treatment developed here, it is possible to make quantitative comparisons with the same inhibitor placed under various physico-chemical situations, i.e., micellar or monolayer states.

Competitive inhibition of lipolytic enzymes. V. A monolayer study using enantiomeric acylamino analogues of phospholipids as potent competitive inhibitors of porcine pancreatic phospholipase A2

For the first time, we have shown that a stereospecific interaction occurs between porcine pancreatic phospholipase A2 and a monomolecular film of amidophospholipid used as inhibitor. Direct binding experiments, using radiolabelled phospholipase A2, showed that 13 times more enzyme was bound to phospholipid films of the L series by comparison with films of the D series. These results were confirmed by indirect binding studies using re-spreading experiments. Kinetic studies of the porcine pancreatic PLA2, using enantiomeric acyl-amino phospholipid analogues, have shown that: (1) inhibitors of the L series are more potent than inhibitors of the D series, (2) inhibitors having a negative charge are more potent than zwitterionic inhibitors, (3) inhibitory power values are greater when evaluated in micellar system than in a the monolayer system, (4) the inhibitory power increases continuously with surface pressure.

Catalysis by a lipase-bearing Rhizopus arrhizus mycelium in (halogeno)fluorinated hydrocarbons

Differentes reactions (esterification, hydrolyse des esters, transacetylation et interesterification) sur un extrait de Rhizopus arrhizus sont effectuees dans des solvants non aqueux. Leurs rendements sont determines, permettant de definir pour la lipase, un systeme de catalyse efficace