| Research Abstract |
(1) Protein Kinases in Postsynaptic Density---Ten protein kinases of Mr=116kDa, 95kDa, 78kDa, 70kDa, 64kDa, 60kDa, 50kDa, 41kDa, 37kDa, and 32kDa have been detected in the postsynaptic density (PSD) from rat brain by means of the activity gel method. Two protein kinases of Mr=50kDa and 60kDa were identified as the alpha and beta subunits of CaM-dependent protein kinase II (CaM-kinase II), respectively. In addition to CaM-kinase II, CaM-independent protein kinases of Mr=95kDa, 78kDa, 70kDa, and 64kDa appeared to be highly enriched in cerebral PSD fraction. These protein kinases were found to be neutral proteins with pI values ranging from 6.7-7.2 when determined by the two-dimentional gel electrophoresis. However, their natural substrates and physiological functions have not been clarified yet.
(2) Purification and Characterization of Brain-specific CaM- dependent Protein Kinase IV (CaM-kinase IV)---CaM-kinase IV has been purified from rat cerebellum. The enzyme was a monomeric enzyme with a molecular weight of 67,000. The enzyme phosphorylated various substrates such as synapsin I, MAP2, myosin light chain, and tyrosine hydroxylase, suggesting that the enzyme is a multifunctional protein kinase. The enzyme underwent autophosphorylation in a Ca^<2+>/CaM-dependent manner. Approximately one mol of phosphate was incorporated into one mol of the enzyme, resulting in a marked stimulation of the enzyme activity. In contrast, CaM-kinase IV was phosphorylated by cAMP- dependent protein kinase, leading to a significant decrease in the enzyme activity. Thus, CaM-kinase IV appears to be under the control of two important intracellular signalling system, the cAMP system and the Ca^<2+> system.
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