Studies on the nature of the amino acid incorporation process of hen oviduct tissue.

A number of recent investigations have been concerned with the relative localization of ribonucleic acid and of protein-synthetic processes within specific structural components of cells (l-9). The results thus far have shown that, after incorporation of radioactive amino acids in vivo or in vitro, the radioactivity is concentrated mainly in the small cytoplasmic particles called microsomes. Preparations of isolated microsomes have also been shown to be most active in incorporating labeled amino acids. The microsomes also account for most of the ribonucleic acid (10-13) of the cells, and this correspondence of ribonucleic acid content and amino acid-incorporating ability is in accord with a proposed relationship between these two properties (1, 2). The present paper describes experiments performed with a tissue highly specialized with respect to protein synthesis, the oviduct of the laying hen. These results also demonstrate a relationship between amino acid-incorporating ability and ribonucleic acid content, but, in contrast to other tissues studied thus far, microsome-like material in this tissue has been found to sediment in low centrifugal fields ( <600 X g in less than 10 minutes as opposed to 20,000 X g or greater for 1 hour or longer (13)). Chemical and cytochemical examinations have shown that the bulk of the cytoplasmic basophilia of the cells is contained in this sedimenting fraction. It has been determined further that this fraction has the greatest tendency to lose previously incorporated amino acids when the specific activity of the free amino acid pool is lowered during the incubation. In contrast, the more soluble proteins continue to increase in specific activity during the period of incubation in the medium in which the specific activity is lowered.