Reversal of Epinephrine Inhibition of Liver Tyrosine Oxidation

Abstract

THYROID hormone interacts with the rat liver tyrosine oxidase system in vitro and in vivo ¹. The site of the inhibition proved to be at the first enzymatic step of the system, namely, tyrosine-α-ketoglutarate transaminase^1,2. Canellakis and Cohen³ first demonstrated an inhibition of this enzyme by epinephrine, using the enzyme from dog liver. Since, under certain conditions, thyroxin and epinephrine are metabolically related⁴, it seemed likely that a demonstration of a similar action of both these hormones on the same enzyme system might provide a basis for exposing a mechanism of hormone action. Some empirical effects of epinephrine upon blood amino-acid levels are known^5–7; but virtually no attempts have been made to explain these results at the molecular level.