The role of cyclic AMP in the induction of tyrosine aminotransferase in neonatal rats: evidence for a release function based on an anomalous effect of puromycin

Abstract

1. 1. In surgically delivered rat infants the administration of puromycin at 3 or 6 hours after delivery leads to potentiation of the postnatal synthesis of tyrosine aminotransferase but puromycin given at delivery effectively prevents production of enzyme activity. 2. 2. Zone sedimentation analysis shows the enzyme activity ‘ induced ’ by puromycin to be of normal size. 3. 3. Hormonal ‘ cocktails ’ containing insulin, hydrocortisone, and adrenaline produce 3 forms of tyrosine aminotransferase in 2-day postnatal rats, adrenaline produces only I form, and puromycin is an apparent inducer in some litters of animals. All these treatments produce tyrosine aminotransferase of the same sedimentation behaviour. 4. 4. Form C of the enzyme is produced by 5 hours after birth of the rat, and when compared with the multiple forms of the enzyme produced by the triple hormonal cocktail, has the same sedimentation characteristics. 5. 5. In a certain proportion of 2-day postnatal rat litters enzyme activity can be increased by adrenaline or puromycin and both agents either are consistently effective or are both ineffective. 6. 6. In ‘ inducible ’ litters, RNase digestion of either liver extracts or the polysomemicrosome fraction increases the enzyme activity in vitro but has no effect in ‘ pre-induced ’ or ‘ non-inducible ’ preparations. 7. 7. The data are interpreted as indicating the operation of a control mechanism working at an enzyme release step in the tyrosine aminotransferase system and taken together with other work it is suggested that this mechanism operates on form C of tyrosine aminotransferase and is mediated at the intracellular level by cyclic AMP.