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Independent Protein Kinases Associated with the Rat Cerebral Synaptic Junction: Comparison with Cyclic AMP‐Dependent and Ca 2+ /Calmodulin‐Dependent Protein Kinases in the Synaptic Junction
Author(s) -
Suzuki Tatsuo,
Fujii Toshihiro,
Tanaka Ryo
Publication year - 1987
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.1471-4159.1987.tb05728.x
Subject(s) - synapsin i , protein kinase a , kinase , phosphorylation , protein phosphorylation , biology , microbiology and biotechnology , calmodulin , biochemistry , adenylate kinase , chemistry , synaptic vesicle , receptor , enzyme , vesicle , membrane
Independent protein kinases in the synaptic junction (SJ) isolated from rat cerebrum were characterized. SJ showed a protein kinase activity, phosphorylating intrinsic proteins, even in the absence of cyclic AMP or Ca 2+ plus calmodulin (CaM) exogenously added. The activity was affected neither by Ca 2+ concentrations in the physiological fluctuation range nor by the addition of specific ligands such as glutamate, aspartate, acetylcholine, and concanavalin A. The activity was not due to cyclic AMP‐dependent protein kinase in SJ, since the activity was not inhibited by an inhibitor protein for cyclic AMP‐dependent protein kinase, and since synapsin I was not specifically phosphorylated whereas cyclic AMP‐dependent kinase appeared to phos‐phorylate selectively the protein in SJ. Phosphorylation of SJ proteins by the independent kinases was about one‐third of that of the Ca 2+ /CaM‐dependent protein kinase intrinsic to SJ. The apparent K m for ATP was estimated to be 700 μ M . Proteins of 16K M r and 117K M r were specifically phosphorylated under the basic condition (in the absence of the substances known to activate specifically protein kinases), as well as six other proteins both under the basic conditions and in the presence of Ca 2+ and CaM. The phosphorylation of 150K M r , 60K M r , 51K M r , and 16K M r SJ proteins was enhanced after prephosphorylation of SJ proteins by intrinsic kinase in the presence of Ca 2+ and CaM. This fact suggested that a part of the independent kinase activity was attributable to the autonomous form of Ca 2+ / CaM‐dependent kinase which was derived from its auto‐phosphorylation, and that the Ca 2+ /CaM‐dependent auto‐phosphorylation affected the microtubules in the postsyn‐aptic region inasmuch as the 16K M r protein occurred in both brain cytosol and microtubule protein fraction prepared from rat brain.