Open AccessLipid vesicles which can bind to protein kinase C and activate the enzyme in the presence of EGTA
Author(s) -
EPAND Richard M.,
STAFFORD Alan R.,
LESTER David S.
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb17190.x
Subject(s) - phosphatidic acid , vesicle , phosphatidylserine , egta , chemistry , glycerol , diacylglycerol kinase , biochemistry , calcium , protein kinase c , enzyme , biophysics , phospholipid , biology , membrane , organic chemistry
Maximal protein kinase C activity with vesicles of phosphatidic acid and 1,2‐dioleoyl‐ sn ‐glycerol is observed in the absence of added Ca 2+ . Addition of phosphatidylcholine to these vesicles restores some calcium dependence of enzyme activity. 1,2‐Dioleoyl‐ sn ‐glycerol eliminates the Ca 2+ ‐dependence of protein kinase C activity found with phosphatidic acid alone. Phorbol esters do not mimic the action of 1,2‐dioleoyl‐ sn ‐glycerol in this respect. This suggests that the 1,2‐dioleoyl‐ sn ‐glycerol effect is a result of changes it causes in the physical properties of the membrane rather than to specific binding to the enzyme. The effect of 1,2‐dioleoyl‐ sn ‐glycerol on the phosphatidic‐acid‐stimulated protein kinase C activity is dependent on the molar fraction of 1,2‐dioleoyl‐ sn ‐glycerol used and results in a gradual shift from Ca 2+ stimulation at low 1,2‐dioleoyl‐ sn ‐glycerol concentrations to calcium inhibition at higher concentrations of 1,2‐dioleoyl‐ sn ‐glycerol. Phosphatidylserine‐stimulated activity is also shown to be largely independent of the calcium concentration at higher molar fractions of 1,2‐dioleoyl‐ sn ‐glycerol. Thus, with certain lipid compositions, protein kinase C activity becomes independent of the calcium concentration or requires only very low, stoichiometric binding of Ca 2+ to high affinity sites on the enzyme. Protein kinase C can bind to phosphatidic acid vesicles more readily than it can bind to phosphatidylserine vesicles in the absence of calcium. Addition of 1,2‐dioleoyl‐ sn ‐glycerol to phosphatidylserine vesicles promotes the partitioning of protein kinase C into the membrane in the absence of added Ca 2+ . There is no isozyme specificity in this binding. These results suggest that a less‐tightly packed headgroup region of the bilayer causes increased insertion of protein kinase C into the membrane. This is a necessary but not sufficient condition for activation of the enzyme in the presence of EGTA.