Abstract
In an effort to elucidate the mechanism of mitochondriogenesis in the liver, the author has intended to examine a possible role of the proteases in mitochondria in regulating the mitochondrial protein metabolism. In the present experiment the existence of a proteolytic activity in the matrix of liver mitochondria of the bullfrog, Rana catesbeiana, was revealed and the properties of this activity were characterized. The results obtained are as follows;
1) A proteolytic activity was found in the mitoplast lysates freed from lysosomal contamination. When the lysates were separated into the matrix and innermembrane fractions, the activity was mostly recovered from the former fraction.
2) The activity when assayed at pH 8.5 was largely inhibited by the treatment of the matrix with 1 mM iodoacetamide, suggesting that a thiol protease is responsible for the majority of this activity.
3) The activity was also inhibited by protease inhibitors such as leupeptin, antipain, chymostatin and E 64-C but not by pepstatin at all. No metal ions were found to be involved in the activity.
4) Among a variety of chemical reagents known to react with amino acid residues, iodoacetamide, dithionitrobenzoate and p-chloromercuribenzoate were effective for inhibiting the activity, while diethylpyrocarbonate and phenylmethylsulfonylfluoride were ineffective.
5) Addition of a series of hydrocarbon compounds, ethylene glycol, glycerol, Triton X-100, sodium lauryl sulfate and polyethylene glycol, to the assay mixture revealed that the activity was decreased with increasing of the chain length of the compounds, implying that the enzyme would be more active in hydrophilic than in hydrophobic environments in situ.
6) When the mitochondrial proteins, glutamate dehydrogenase, cytochrome c and cytochrome c oxidase and cytochrome c oxidase in the inner mitochondrial membrane, were subjected to hydrolysis by this activity, only purified cytochrome c oxidase was found to be degraded prominently.
