Template stability of some enzymes in rat liver and hepatoma.

Abstract

Normal rats, or rats bearing the Reuber H-35 hepatoma and subjected to portacaval shunts, were fed a protein-free diet for several days and then intubated with hydrolyzed casein to initiate induction of amino acid-catabolizing enzymes. The inhibitory effects of actinomycin D on the synthesis of certain of these enzymes in the liver and tumor were determined at successive 3-hr intervals up to 21 hr after the initial dose of casein hydrolysate. The period during which induction of a given enzyme was insensitive to actinomycin D was assumed to be the lifetime of the RNA template for that enzyme. The data indicate that the template lifetimes for three enzymes are as follows: serine dehydrase, 6-8 hr; ornithine transaminase, 18-24 hr; tyrosine transaminase, less than 3 hr. In contrast to these measurements in normal liver, the template lifetime for serine dehydrase in two hepatomas was found to be less than two hours in the Reuber H-35 and greater than two weeks in the Morris 5123.