Substrate proteins for calmodulin-sensitive and phospholipid-sensitive Ca2+-dependent protein kinases in heart, and inhibition of their phosphorylation by palmitoylcarnitine.

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Abstract
At least 2 substrate proteins for phospholipid-sensitive Ca2+-dependent protein kinase and at least 6 substrates for calmodulin-sensitive Ca2+-dependent protein kinase were identified in the cytosol of the guinea pig heart. In the particulate subfractions enriched in nuclei, mitochondria microsome or plasma membrane, no substrates for the phospholipid-sensitive enzyme were demonstrated but at least 4 substrates for the calmodulin-sensitive enzyme were identified. Phospholipid, acting independently of calmodulin, may be involved in the regulation of Ca2+-dependent protein phosphorylation in the heart. Phosphorylation of endogenous substrates for the 2 enzyme systems was effectively inhibited by palmitoylcarnitine. When histone was used as exogenous substrate, the carnitine ester inhibited the cardiac phospholipid-sensitive Ca2+-dependent protein kinase but not the cardiac cAMP-dependent and GMP-dependent protein kinases. Inhibition of the Ca2+-dependent phosphorylation of cardiac proteins, regulated by either phospholipid or calmodulin, is probably related in part to the great increase in this fatty acid metabolic intermediate in the ischemic heat.