Transport of proteins into mitochondria: a high conservation of precursor uptake and processing system.

Ornithine transcarbamylase (EC 2.1.3.3) of rat (Rattus norvegicus var. albus) liver, a urea cycle enzyme, is synthesized extramitochondrially as a larger precursor which is transported posttranslationally into mitochondria and processed to the mature enzyme. The precursor synthesized in vitro was taken up and processed to the mature enzyme by isolated pigeon (Columba livia var. domestica) liver and frog (Rana catesbeiana) liver mitochondria. Carp (Cyprinus carpio) liver mitochondria could also process the precursor. These results indicate that the mitochondrial transport and processing activities are conserved between mammalian and bird, amphibian or fish systems. However, attempts to demonstrate the precursor uptake and processing by Saccharomyces cerevisiae mitochondria were unsuccessful.