Regulation of liver tyrosine aminotransferase activity in inbred strains and mutant mice. II. Studies on the starvation-induced enzyme adaptation

Abstract

The activity of liver tyrosine aminotransferase (TA) (L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5) in C57BL/6J mice was elevated at 0900 h two- to three-fold above the control level after 48 h of fasting. In DBA/2J mice, TA activity remained low during 48 h of fasting. However, enzyme activity could be increased in fasting DBA/2J mice by the administration of either hydrocortisone or nicotinamide. The administration of glucose to fasting C57BL/6J mice caused a rapid reduction of enzyme activity to the basal level. When hydrocortisone was administered simultaneously with the glucose, the enzyme activity was maintained (approximately 73% of the untreated 1330-h control values) and was elevated about twofold above the enzyme activity in the glucose-treated mice. Multiple injections of cycloheximide (1 μg/g body weight dose) caused a slight reduction (40%) of the starvation-induced enzyme adaptation. In adrenalectomized C57BL/6J mice, TA activity remained low during a 60 h fasting period. Significant strain differences were also demonstrated in the regulation of the apoenzyme and holoenzyme levels in C57BL/6J and DBA/2J mice after 48 h of fasting.