Two Mitochondrial Matrix Proteases Act Sequentially in the Processing of Mammalian Matrix Enzymes

• Published in: Proceedings of the National Academy of Sciences - PNAS 1988-10, Vol.85 (20), p.7536-7540
• Main Authors: Kalousek, Frantisek, Hendrick, Joseph P., Rosenberg, Leon E.
• Format: Article
• Language: English
• Subjects: Amino acids; Analytical, structural and metabolic biochemistry; Animals; Biochemistry; Biological and medical sciences; Carboxy-Lyases - metabolism; Data processing; Enzyme Precursors - biosynthesis; Enzyme Precursors - metabolism; Enzymes; Enzymes and enzyme inhibitors; Ethylmaleimide - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Hydrolases; Liver; malate dehydrogenase; Malate Dehydrogenase - metabolism; Metal ions; Methylmalonyl-CoA Decarboxylase; Mitochondria; Mitochondria, Liver - enzymology; ornithine carbamoyltransferase; Ornithine Carbamoyltransferase - biosynthesis; Ornithine Carbamoyltransferase - metabolism; Peptide Hydrolases - isolation & purification; Peptide Hydrolases - metabolism; Protein precursors; Protein Sorting Signals - metabolism; Proteins; Rats
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.85.20.7536

The imported precursors of the mammalian matrix enzymes malate dehydrogenase [(S)-malate:NAD+ oxidoreductase, EC 1.1.1.37] and ornithine transcarbamylase (carbamoyl-phosphate:L-ornithine carbamoyltransferase, EC 2.1.3.3) are cleaved to their mature subunits in two steps, each catalyzed by matrix-localized processing proteases. The number and properties of these proteases are the subjects of this report. We have identified and characterized two distinct protease activities in a crude matrix fraction from rat liver: processing protease I, which cleaves these precursors to the corresponding intermediate form; and processing protease II, which cleaves the intermediate forms to mature subunits. Protease I is insensitive to chelation by EDTA and to inactivation with N-ethylmaleimide; protease II is inhibited by 5 mM EDTA and is inactivated by treatment with N-ethylmaleimide. We have prepared from mitochondrial matrix an 800-fold-enriched protease I fraction free of protease II activity by using the following steps: ion exchange, hydroxyapatite, molecular sieving, and hydrophobic chromatography. Using similar procedures, we also have prepared an approximately 2000-fold-enriched protease II fraction, which has a trace amount of contaminating protease I. This enriched protease II fraction has little or no cleavage activity toward mitochondrial precursors but rapidly and efficiently converts intermediate forms to mature size. Finally, we show that protease I alone is sufficient to cleave the precursor of a third nuclear-encoded mitochondrial protein subunit--the β subunit of propionyl-CoA carboxylase [propanoyl-CoA:carbon dioxide ligase (ADP-forming), EC 6.4.1.3]--to its mature size.