Polyphosphoinositides as activators of PKC-dependent synapsin I phosphorylation

The effect of PIP2 and diacylglycerol (products of polyphosphoinositide turnover) on the activation level of phosphorylation of the human brain neurospecific protein SI by PKC from the same source was studied. The apparent activation constant of the phosphorylation process was shown to decrease in the presence of PIP2 from 1.1 micrograms/ml for PI and from 0.8 micrograms/ml to 0.6 microgram/ml for PS; the value of 0.4 microgram/ml in the latter case was detected merely after the addition of DOG into the reaction mixture. Polyphosphoinositides are suggested to play a role in activating PKC-mediated phosphorylation of SI in nerve terminals.