Repression of enzyme synthesis at the translational level and its hormonal control.

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Abstract
Administration of stressing agents (tyrosine, Celite) to adrenalectomized rats initiates a highly selective repression of the synthesis of hepatic tyrosine-[alpha]-keto-glutarate transaminase. The enzyme level falls with a t1/2 about 2.5 hr. Immunochemical measurement of the rate of enzyme synthesis indicates that it is reduced essentially to zero in stressed, adrenalectomized rats, whereas labeling of total liver soluble proteins is unaffected. Actinomycin does not itself influence the enzyme level, but it blocks the stress-initiated repression of enzyme synthesis, indicating that repression acts at the translational level, whereas initiation of repression involves transcriptional processes. The stressing agents are ineffective in hypophysectomized rats, implicating an hormonal factor of pituitary origin in the initiation of repression.