The specific activity of
leucine transaminase was measured in supernatants of liver, skeletal muscle (gastrocnemius), and kidney homogenates obtained from fed, starved, and
protein-deprived rats. After 12 h of
starvation, there were slight reductions in
leucine transaminase activity of both muscle and kidney tissues. When
starvation was prolonged to 1 full day, the activity of this
enzyme increased by approximately twofold in both muscle and kidney. Prolongation of fasting to 5 days resulted in an additional increase in specific activity of
leucine transaminase in muscle. During the entire 5 days of
starvation,
leucine transaminase activity remained unaltered in liver of starved rats.
Protein deprivation for 1 or 5 days resulted in significant reductions in specific activity of
leucine transaminase in skeletal muscle.
Protein deprivation did not produce a remarkable effect on the activity of this
enzyme in kidney or liver tissue. The results of this study, together with those previously obtained, indicate that within our experimental conditions increased oxidation of
leucine in skeletal muscle of starved rats is not initially related to an alteration in activity of
leucine transaminase. When caloric deficiency is prolonged, the potential for transamination is also increased. These adaptive changes increase the ability of skeletal muscle to use
leucine as a metabolic fuel.