ACTION OF CYCLIC ADENOSINE 3′,5′ MONOPHOSPHATE ON L-14C-LEUCINE INCORPORATION IN A SYSTEM OF ROUGH MICROSOMES FROM BOVINE THYROID GLAND

Abstract

ABSTRACT The effect of cAMP and varying concentrations of potassium (18–72 mM) on the incorporation of L-14C-leucine into TCA-precipitable protein was studied in a cell-free system comprising rough thyroid microsomes. cAMP (2 mm) alone or in combination with theopylline increased the incorporation of leucine into ribosome-bound (after DOC treatment) and extra-vesicular material, but had no significant effect on the DOC-released intravesicular material. Increase of the K+ concentration from 18 mm to 72 mm affected the incorporation of leucine into the microsomal compartments in much the same way as cAMP did. The effect of cAMP and potassium seems to be due in partly to enhanced activation of amino acids, since in a system of pH5 fraction and cell sap, both cAMP and K+ increased the incorporation of 14C-leucine into cold TCA-precipitable material. Experiments with 14C-leucyl-tRNA as a marker suggest that the effect of cAMP and K+ is a consequence not only of increased activation of amino acids, but also of increased binding of activated amino acyl-tRNA to ribosomes.