Kinetic Anomalies Associated with Phospholipase A2 Hydrolysis of Micellar Substrates
It is well known that Phospholipase A2 hydrolyzes micellar substrates at considerably faster rates than monomeric substrates. The origin of this interfacial activation is a subject of considerable importance in understanding the mechanism of action of lipolytic enzymes. Crotalus adamanteus Phospholipase A2 exhibits “normal” Michaelis kinetics with monomeric substrates (12) and with micellar substrates at concentrations well above the critical micelle concentration (cmc) (13). However, at concentrations near the cmc anomalous velocity vs substrate concentration plots are observed which are parabolic rather than hyperbolic (11, 13). We have noted this phenomenon for several different substrates and for Phospholipases A2 from various sources and for cabbage Phospholipase D, and have empiricially determined that such anomalous regions give linear plots of v1/2 vs substrate concentration. To our knowledge no satisfactory explanation for these anomalous regions have been presented. The purpose of this paper is to explore various explanations for this behavior and to propose a model for substrate micellization which satisfactorily predicts such anomalous kinetics.
KeywordsCritical Micelle Concentration Micelle Formation Polar Head Group Anomalous Region Oblate Ellipsoid
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