The hemoglobin molecule is composed of two 01 peptide chains, two S peptide chains, and four heme groups. In the rabbit reticulocyte the peptide chains are synthesized on the polyribosomes. The mechanism of assembly of the final molecule from the component polypeptide chains and heme groups is of current interest in several laboratories. One particular problem is to deter mine the nature of the soluble chain intermediates in hemoglobin completion. The current report documents evidence for a soluble fraction in rabbit reticulocytes containing newly synthesized Q: chains which appear to be intermediates in hemoglobin construction.

EXPERIMENTAL: Reticulocytes were obtained from the blood of phenylhydrazine treated rabbits and washed once with a modified saline solution (Allen and Schweet, 1962). In order to study the soluble polypeptide products in hemoglobin synthesis the reticulocytes were pulse-labeled with 3H leucine. The washed cells were suspended in a solution having the following composition; 0.5 nmole each of 19 amino acids except leucine, 50 wmoles Tris* HCl pH 7.5, 0.4 pmole Fe (NH $2 (S04) 2, 273 timoles NaCl, 10.5 umoles KCl, 16 pmoles MgC12, 0.25 ml of packed cells, and 0.025 Fmole L-leucine-4, 5-3H(5000 cccuries/pmole) in a total volume of 2.9 ml. The mixture was incubated for 5 min at 37'. The labeled cells were centrifuged and lysed as previously described (Allen and Schweet, 1962). The ribosomes were removed from the lysate (90 min at 105,000 X g). In order to determine the electrophoretic nature of the 1