The control of hemoglobin synthesis. A comparison of the role of heme in rabbit bone marrow and reticulocytes.

The incorporation of L-[U-14C]lysine into the Q and /3 chains of hemoglobin has been compared in acetylphenylhydrazineinduced rabbit reticulocytes and normal and acetylphenylhydrazine-induced rabbit marrow. Evidence for a pool of Q chains and a/3 dimers in both reticulocytes and marrow cells was found in (a) an LY: /3 specific activity ratio of less than 1.0 in purified hemoglobin, (b) the relative losses of a! and /3 chain radioactivity on purification of the hemoglobin, (c) the radioactivity elution profile observed on gel filtration of the ribosome-free hemolysate, and (d) the effects of hemin added to the postincubation hemolysate. However, the data also indicated that the pool of a~ chains is smaller in the marrow cell than in the reticulocyte. In both groups of cells, addition of hemin to the incubation medium was followed by greater synthesis of o( and /3 chains than was observed in the control cells. In addition, in marrow cells it was associated with virtually complete disappearance of the LY chain and a@ pools, as evidenced by an increase in the o(:fl specific activity ratio in purified hemoglobin to almost 1.0 and by the disappearance of the high specific activity minor peak from the gel elution profile. On the basis of pulse labeling and chase experiments it was confirmed that both the pool of 01 chains and a/3 dimers exist as intermediates in the pathway of hemoglobin biosynthesis. However, in the reticulocyte the radioactive CY chain pool could be chased into hemoglobin to only a limited extent, in contrast to the marrow where almost complete transfer of radioactivity into hemoglobin occurred during the chase period. It is suggested that in the developing erythroid cell heme serves to promote hemoglobin synthesis by (a) promoting the synthesis of a! and p chains and (b) promoting the conversion of afi dimers to the hemoglobin tetramer. In addition it also serves to coordinate the synthesis and assembly of 01 and /3 chains.