Tyrosine aminotransferase activity in liver of pyrazole-treated rats

Abstract

We have shown previously [l] that pyrazole administration to rats inhibits the hepatic activity of tryptophan oxygenase [EC 1.13.1.121 probably by reducing the degree of heme saturation of the apoenzyme and thus the enzyme biosynthesis. As pyrazole also affects catalase [EC 1.11.1.61 [2] , a specific effect of this compound on hemoprotein enzymes was suggested. However, the data obtained did not allow us, to exclude a more general effect of pyrazole on enzyme synthesis. It seemed therefore of interest to test whether pyrazole also affects the activity of tyrosine aminotransferase [EC 2.6.1.51, enzyme which, although requiring pyridoxal phosphate and not heme, has, like tryptophan oxygenase, a rapid turn-over in the liver [3] and is also inducible by cortisol [4]. The present results show that pyrazole administration to rats modify the induction time course of tyrosine aminotransferase by cortisol in a way which is similar to that described after administration of known inhibitors of protein synthesis [5,6].