In many lipid systems, the activity of protein kinase C (PKC) exhibits a pe
ak followed by a decline as the mol % of one component is increased. In the
se systems, an increase in one lipid component is always at the expense of
another or accompanied by a change in total lipid concentration. Here we re
port that in saturated phosphatidylserine (PS)/phosphatidylcholine (PC)/dia
cylglycerol (DAG) mixtures, increasing PS or DAG at the expense of PC revea
led an optimal mol % PS, dependent on mol % DAG, with higher mol % PS dimin
ishing activity. The decrease at high mol % PS is probably not attributable
simply to more gel-phase lipid due to the higher melting temperature of sa
turated PS versus PC because a similar peak in activity occurred in unsatur
ated lipid systems. Increasing the total lipid concentration at suboptimal
mol % PS provided the same activity as higher mol % PS at lower total lipid
concentration. However, at optimal mol % PS, activity increased and then d
ecreased as a function of total lipid concentration, PKC autophosphorylatio
n also exhibited an optimum as a function of mol % PS, and increasing the P
RC concentration increased the mol % PS at which activity decreased, both f
or autophosphorylation and for heterologous phosphorylation. Formation of t
wo-dimensional crystals of PKC on lipid monolayers also exhibited a peak. a
s a function of mol % PS, and the unit cell size of the crystals formed shi
fts from 50 x 50 Angstrom at low mol % PS to 75 x 75 Angstrom at higher PS.
Collectively, these data suggest the existence of optimal lipid compositio
ns for PKC activation, with increased quantity of these domains serving to
dilute out enzyme-substrate aggregates and/or enzyme-enzyme aggregates on t
he lipid surface.