Incorporation in vitro of labeled amino acids into proteins of rabbit reticulocytes.

labeled glycine, L-histidine, L-leucine, and L-lysine into the proteins of rabbit reticulocytes. In preliminary experiments the incorporation into the hemoglobin isolated from the reticulocytes was determined. But, after it was found that plasma contains factors accelerating amino acid incorporation, it was decided to proceed as rapidly as possible toward the identification of these factors; we have, therefore, measured incorporation into the total proteins of the reticulocytes, since isolation of the hemoglobin was time-consuming. The results obtained with hemoglobin and with the total proteins are essentially the same, indicating that the other proteins of the reticulocytes incorporate amino acids at approximately the same rate as hemoglobin. Production of Reticulocytosis-Reticulocytosis was produced in adult rabbits by a modification of the method of London et al. (2). 1 ml. of a neutralized 2.5 per cent aqueous solution of phenylhydrazine hydrochloride was injected subcutaneously each day for a week; over 90 per cent of the