Protein Synthesis in the Rat Anterior Pituitary. I. Interrelationship of Amino Acid Uptake to Protein Synthesis

Abstract

In the rat anterior pituitary incubated in vitro, labeled amino acid uptake proceeded exponentially with time until a constant level was reached, whereas amino acid incorporation into protein after a slight lag was linear. When trace levels of a 3H-amino acid mixture or of 3H-leucine were added to the incubation medium a large percentage of all the amino acid radioactivity found in the tissue at 150 min was in protein. In the presence of plasma levels of unlabeled amino acids in the medium, including the counterparts of the radioactive amino acids, the uptake of a 3H-amino acid mixture, 3Hleucine or 14C-glutamic acid increased steadily as the medium concentration of that amino acid(s) was raised. Incorporation into protein increased in proportion to the enhanced uptake over a variable range of amino acid concentrations. If the medium amino acid concentration was held constant, then, on a per mg basis, uptake and incorporation of a 3H-amino acid mixture increased as the weight of the pituitary decreased or as the pituitary was damaged. These studies indicate that the pituitary incubated in vitro is capable, under conditions leading to increased amino acid uptake, of responding with enhanced levels of incorporation into protein. (Endocrinology88: 540, 1971)