XXXX -modulated protein kinase activity from human spleen. II. Interaction with phospholipid vesicles.

@entity4357 @entity3634
Phosphorylation of endogenous and artificial protein substrates by protein kinase P is stimulated by @entity4357 or @entity3634 (D. J. Klemm, and L. Elias (1987) J. Biol. Chem. 262, 7580-7585; L. Elias and A. Davis (1985) J. Biol. Chem. 260, 7023-7028). Stimulation of protein kinase P activity required phospholipid vesicles rather than free phospholipid molecules. Protein kinase P activity increased as the @entity4357 content of the vesicles was raised from 20 to 100%; no stimulation was detected below 20% @entity4357 . This suggests that a vesicle surface rich in @entity4357 is required for enzyme activation. Maximum activation of protein kinase P activity showed an optimum value with respect to phospholipid concentration, with both endogenous and artificial protein substrates. The phospholipid concentration at which optimal enzyme activity occurred shifted in response to the concentration of protein substrate, but not enzyme concentration. Therefore, the density of substrate molecules on the surface of phospholipid vesicles is a critical feature of protein kinase P stimulation. Binding of protein kinase P to vesicles was independent of micelle composition, but the binding of the artificial substrate, histone H2B, was specific for vesicles containing @entity4357 or @entity3634 , and increased as the content of @entity4357 was increased. Thus, an important feature of protein kinase P activation appeared to be the specific binding of protein substrate to phospholipid vesicles.
