Vol. 110, No. 2, 1983 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS January 27, 1983 Pages 499-503 TRANSPORT OF THE PRECURSOR FOR RAT LIVER GLUTAMATE DEHYDROGENASE INTO MITOCHONDRIA "IN VITRO" Vicente Miralles#, Vicente Felipo#, Jo& Herndndez-Yago and Santiago Grisolia Instituto de Investigaciones Citoldgicas de la Caja de Ahorros de Valencia Amadeo de Saboya, 4, Valencia, Spain Received October 11, 1982 SUMMARY Glutamate dehydrogenase of rat liver, a mitochondrial matrix enzyme, is synthesized in a larger precursor form in a rabbit reticulocyte cell-free system. When this pre- cursor was incubated with isolated mitochondria in the absence of protein synthesis, it was processed to the mature form and rendered protease-resistant during incubation with mito- chondria. The majority of intramitochondrial proteins are initial- ly synthesized on cytoplasmic ribosomes (1) and, therefore, must be transported across an intact outer membrane before reaching their final destination. We (2) and Mihara et al. -- (3) reported that glutamate dehydrogenase of rat liver is synthesized "in vitro" as a precursor larger than the mature form. Hence, pre-glutamate dehydrogenase must be transferred across both the outer and inner membranes of mitochondria to reach its final location in the mitochondria. We further showed that a mitochondrial extract from rat liver processed the precursor synthesized "in vitro" to the mature form (2). We report here that the precursor of # Vicente Miralles and Vicente Felipo are "Reina Dofia Sofia" Fellows of this Institute. 499 0006-291X/83/020499-05$01.50/0 Copyright 0 1983 by Academic Press, Inc. AN rights of reproduction in any form reserved.