In vitro activation of bovine adrenal tyrosine hydroxylase by rabbit skeletal muscle actin: evidence for a possible role of cytoskeletal elements as an activator for cytoplasmic enzymes

Abstract

Tyrosine hydroxylase prepared from the soluble fraction of bovine adrenal medulla was markedly activated by rabbit skeletal muscle G-actin, and this activation was accompanied by a decrease in the apparent K m of the enzyme for the pterin cofactor. The activating effect of G-actin on the soluble enzyme was still observed in the medium containing a high concentration of salt or excess amounts of proteinase inhibitors. Furthermore, this effect was not affected by either cytochalasin B or DNase I. These results therefore suggest that G-actin interacts with the enzyme molecule at the binding site(s) different from that involved in actin polymerization, and that it causes the activation of the soluble enzyme as a result of an allosteric alteration in the enzyme structure, thus giving rise to the possibility that cytoskeletal elements play an important role in the regulation of catecholamine synthesis as a factor modulating the activity of cytoplasmic tyrosine hydroxylase.