Ca(2+)-dependent phosphorylation of synapsin I as a possible regulatory mechanism of neurosecretion.
Phosphorylation of homogeneous synapsin I isolated from human brain by Ca2+, phospholipid-dependent protein kinase (protein kinase C) from the same source was studied. The inhibitory effect of calmodulin on this process was demonstrated. The kinetics of activation of synapsin I phosphorylation by acidic phospholipids, phosphatidylserine and phosphatidylinositol, in the absence and presence of phosphatidylinositol-4,5-bisphosphate and diacylglycerol was compared. The proteolytic effect of degradation of the synapsin I molecule phosphorylated by Ca2+, calmodulin-dependent protein kinase II was revealed. No proteolysis of synapsin phosphorylated under similar conditions either by protein kinase C or cAMP-dependent protein kinase was detected. In view of the process specificity, the physiological significance of the observed effect is suggested. The inter-relationship between two ways of neurosecretion regulation is discussed: an earlier known, conventional way, mediated by synapsin I phosphorylation by Ca2+, calmodulin-dependent protein kinase II, and another one, mediated by synapsin I phosphorylation by protein kinase C. The modulating role of polyphosphoinositides in the PK C-dependent way of regulation is considered.
Severin
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Research Center of Molecular Diagnostics, U.S.S.R. Ministry of Health, Moscow.
Moskvitina
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EL
Gubin
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Kiselev
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D001921:Brain / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D007700:Kinetics; D009419:Nerve Tissue Proteins / Q000302:isolation & purification / Q000378:metabolism*; D010449:Peptide Mapping; D010743:Phospholipids / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D016704:Synapsins
D009419:Nerve Tissue Proteins; D010743:Phospholipids; D010750:Phosphoproteins; D016704:Synapsins; D011493:Protein Kinase C