Studies on New Intracellular Proteases in Various Organs of Rat

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Abstract
To study the role of group‐specific protease in enzyme degradation, alternation of its activity under various physiological conditions was examined. Studies on the distribution of group‐specific protease in various organs of rats showed high activity in skeletal muscle and the muscle layer of small intestine, and rather low activity in liver. The activity varied in different muscles, but red muscle tended to have higher activity than white muscle. Activity was much lower in the muscles of the stomach and colon than in those of the small intestine. Group‐specific protease in skeletal muscle increased under various dietary conditions (starvation, protein‐free diet or high protein diet), but the activities in the muscle layer of the small intestine and liver were not greatly influenced by dietary conditions. None of the hormones tested (i.e. hydrocortisone, glucagon, insulin, growth hormone and estrogen) influenced the activity of group‐specific protease in liver. The level of group‐specific protease in skeletal muscle was increased markedly fifteen days after denervation, with a reciprocal decrease in the level of muscle phosphorylase, which is a good substrate of the protease. Liver protease activity appeared in the late suckling period. The activity in skeletal muscle was high at the time of birth and attained the adult level 3 weeks after birth. The activity in the muscle layer of the small intestine did not change after birth. Thus the mechanisms for evoking these three specific proteases during development are apparently different. The activity of liver protease began to decrease approximately 12 h after partial hepatectomy and reached a minimum after about 72 h. Recovery of the protease activity was very slow and activity had not returned to the normal value 7 days after the operation. This observation seems to be consistent with the fact that there is little or no protease activity in liver in the neonatal period.