This chapter discusses brain CaM-kinase II with a particular focus on its unique regulatory properties, its regulation in cultured brain cells, and its physiological functions. CaM-kinase II has widespread tissue distribution as oligomeric isozyme forms and is particularly abundant in the brain. In certain regions of the brain, such as hippocampus, it constitutes up to 2% of total protein, which probably makes it the most abundant enzyme in these tissues. CaM-kinase II is localized presynaptically where it is involved in Ca2+-dependent regulation of neurotransmitter biosynthesis and exocytosis. At excitatory synapses in forebrain, there is a thickening of the postsynaptic membrane called the postsynaptic density (PSD), and CaM-kinase II constitutes about 30–50% of the protein in the PSD. These excitatory synapses are subject to a usage-dependent enhancement of synaptic transmission called long-term potentiation (LTP)—a popular model for learning and memory.
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