Effects of Puromycin and Actinomycin D on the Increase of Cystathionase and Cysteine Sulphinic Acid Decarboxylase Activities in the Liver of Thyroidectomized Rat

Abstract

PREVIOUS investigations carried out in this laboratory have shown that the concentration of two cytoplasmic rat liver enzymes dependent on pyridoxal phosphate, namely, cysteine sulphinic acid (CSA) decarboxylase (L. cysteine sulphinate carboxylase E.C. 4.1.1.29) and cystathionase (L. homoserine hydrolyase E.C. 4.2.1.15), are adaptively increased in thyroidectomized animals^1,2. The events underlying these changes in response to thyroidectomy are not known; however, we have suggested that the increase of activities may be attributable to an increased biosynthesis of the two apoenzymes³, and recently we have obtained results which agree with such a hypothesis⁴. The experiments reported here were undertaken in order to determine whether these increases are prevented by injections of inhibitors of protein biosynthesis—puromycin⁵—and of the DNA-directed RNA synthesis—actinomycin D (ref. 6). Both experiments were carried out in similar conditions except that in the first rats were given intraperitoneal injections of puromycin daily for 4 days at a dose each of 5 mg/100 g of body weight, whereas in the second actinomycin D was injected by the same route and for the same time at a dose of 3 µg/100 g of body weight. The animals were killed 4 h after the last injection. The amounts of inhibitor injected were chosen taking into consideration the report of Weber et al.⁷ and the results of preliminary assays.