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A Protein Modulator Stimulates C Kinase‐Dependent Phosphorylation of a 90K Substrate in Synaptic Membranes
Author(s) -
Kligman Douglas,
Patel Jitendra
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb02862.x
Subject(s) - phosphorylation , biochemistry , protein kinase a , kinase , protein phosphorylation , substrate (aquarium) , chemistry , protein kinase c , proteolysis , biology , biophysics , enzyme , ecology
We have identified and partially purified an acidic, heat‐stable, noncalmodulin protein from bovine brain cytosol that stimulates Ca 2+ ‐dependent phosphorylation of an M r 90K substrate in crude rat brain synaptic membranes. We show that this modulator of phosphorylation (MOP) enhances Ca 2+ ‐ and phospholipid‐dependent protein kinase (C kinase) phosphorylation of this 90K substrate. The 90K substrate is a higher M r form of an 87K substrate that is a major C kinase substrate in rat brain. The Ca 2+ ‐dependent phosphorylation of both substrates is inhibited by the Ca 2+ ‐binding proteins S‐100 and calmodulin. Both substrates yield phosphopeptide fragments of M r 9K and 13K after limited proteolysis with V8 protease. Two‐dimensional polyacrylamide gel electrophoresis reveals that they have similar acidic iso‐electric points (pI 5.0). MOP enhances Ca 2+ ‐dependent phosphorylation of the 90K substrate whereas the phosphorylation of 87K is diminished. This reciprocal relationship suggests that the mobility of the 87K substrate in sodium dodecyl sulfate‐polyacrylamide gels is decreased to 90K with increasing phosphorylation. MOP may be a novel protein modulator of C kinase‐mediated phosphorylation in the nervous system.