JBC, Vol. 254, Issue 24, 12542-12546, Dec, 1979
Ca2+-dependent protein phosphorylation of purely cholinergic Torpedo synaptosomes
D. M. Michaelson and S. Avissar
Preincubation of intact, purely cholinergic Torpedo synaptosomes with
[32P]Pi results in the incorporation of 32P into about 10 specific
proteins. Depolarizing the Torpedo synaptosomes by a high K+ buffer or
treatment with the Ca2+ ionophore A23187 result in Ca2+ uptake, in
acetylcholine (ACh) release, and in a marked increase of 32P incorporation
into a specific protein band with an apparent subunit molecular weight of
100,000 (band alpha). The kinetics of synaptosomal 45Ca2+ uptake, of 32P
incorporation into band alpha, and of ACh release is similar and reach
maximal values about 45 s after the synaptosomes have been treated. Sr2+
and Ba2+ can replace Ca2+ in evoking both K+ depolarization-dependent ACh
release and 32P incorporation into band alpha. The effectiveness of these
ions (Ca2+ greater than Sr2+ greater than Ba2+) is similar in both cases.
The data presented suggest that Ca2+ accumulation by Torpedo synaptosomes
leads to an increase in the phosphorylation of a specific protein and to
ACh release. This phosphoprotein may be involved in the regulation of
presynaptic processes which underly ACh release.
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