Processing of pre-ornithine transcarbamylase requires a zinc-dependent protease localized to the mitochondrial matrix

Abstract

Proteolytic processing of the larger precursor of the rat liver mitochondrial matrix enzyme, ornithine transcarbamylase, has been studied in a cell free system using in vitro -synthesized precursor and various submitochondrial fractions. The protease responsible for cleavage to mature-sized enzyme fractionates with matrix marker enzymes. Maximal catalytic activity of this matrix protease requires approximately 0.1 mM Zn 2+ , a concentration known to be in the physiological range for this divalent cation in intact mitochondria. Certain other divalent metal ions (Co 2+ and Mn 2+ ) also stimulate this protease activity, while 1,10-phenanthroline, a divalent metal ion chelator, inhibits the protease. We conclude that proteolytic cleavage by a zinc-dependent protease in the mitochondrial matrix of rat liver is a required step in the conversion of pre-ornithine transcarbamylase to the mature subunit.