Induction of tyrosine transaminase activity by hydrocortisone in vitamin B-6-deficient rats
Puskar, T.; Tryfiates, G.P.
Journal of Nutrition 104(11): 1407-1415
1974
ISSN/ISBN: 0022-3166 PMID: 4153659 Document Number: 82090
The effects of vitamin B-6 deficiency on hormonal induction of tyrosine transaminase and the synthesis of proteins in rat liver were studied. Hydrocortisone hemisuccinate was given intraperitoneally and the activity of tyrosine transaminase and incorporation of 3H-labelled L-amino acids into liver proteins and into tyrosine transaminase were estimated. Vitamin B-6 deficiency directly affected both enzyme induction and protein synthesis. The specific activity of hepatic tyrosine transaminase was 3 times as much in rats fed freely or pair-fed controls on stock diet as in deficient rats. Induction of the enzyme by hydrocortisone in vitamin B-6 deficiency was characterized by: an early peak induction time of 3.5 to 6 h when protein synthesis in vivo was normal; a delayed incorporation of label into protein, including tyrosine transaminase (8 to 10 h); an increased rate of protein synthesis; and a failure of cycloheximide to block the rise in enzyme activity in spite of its effective inhibition of incorporation of label into liver proteins. On the other hand, hormonal induction of the enzyme in controls was characterized by: the occurrence of peak enzyme induction, protein synthesis in vivo, and antitransaminase-precipitable radioactivity after 6 h treatment with the hormone; and by effective inhibition by cycloheximide of both the rise in enzyme activity and the incorporated radioactivity in vivo into liver proteins, including transaminase.