Hepatic Tyrosine Transaminase Rhythm: Interaction of environmental lighting, food consumption and dietary protein content

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Abstract
Hepatic tyrosine transaminase activity was measured over a 24-hour period in animals maintained under three environmental situations: normal lighting (lights on from 9 AM to 9 PM) and ad libitum dietary protein; reversed lighting (lights on from 9 PM to 9 AM) and ad libitum dietary protein; and normal lighting and a nonprotein diet, with protein added at various times during the day. In each case, the increase in tyrosine transaminase activity was not observed until after the initial ingestion of protein. These results support the hypothesis that the daily rhythm in the activity of this enzyme in rat liver is generated by the cyclical ingestion of protein.