REGIONAL AND SUBCELLULAR DISTRIBUTION OF PROTEIN CARBOXYMETHYLASE IN BRAIN AND OTHER TISSUES

Protein carboxymethylase, an enzyme that transfcrs the methyl group of S-adenosyl-L-methionine to carboxyl groups of proteins and endogenous acceptor proteins were examined in nerve and endocrine tissues. The highest protein carboxymethylase activity was found in the brain, followed by the testis, pituitary and heart. On the other hand, the tissue with the highest level of endogenous substrate(s) was the pituitary. The nearly identical specific activity ratio for two different protein substrates in all tissues examined, suggests that one enzyme is responsible for carboxymethylase activity in different tissues. The subcellular distribution of the enzyme in brain showed a high concentration in the soluble fraction, presumably representative of the enzyme in the cytosol of cell bodies. Considerable enzyme activity was also found in brain synaptosomes which was increased by osmotic lysis. Protein carboxymethylase was shown to accumulate proximally to a ligation of the rat sciatic nerve. A possible physiological role for protein carboxymethylase in neuronal function is discussed.