Studies of the terminal stages of hemoglobin synthesis: I. Stimulation of globin chain synthesis by native hemoglobin subunits

Abstract

A homologous canine reticulocyte cell-free system was utilized to determine the effects of native hemoglobin subunits on the synthesis of the α and β chains of globin. The addition of either αH or βH in concentrations of 10-3-10-5 M to the cell-free system caused a reproducible increase in synthesis of globin to a maximum of 1½ times that of control values. Tetrameric hemoglobin and other nonglobin proteins in similar concentrations did not produce this effect. While the effect of added αH was to primarily increase β globin synthesis, thus lowering the α/β ratio, βH increased the rates of synthesis of both α and β globin equally. Hemin, which increases protein synthesis but does not change the α/β ratio, was not responsible for the observed changes. These findings suggest that native αH and βH are each independently capable of influencing the rate of globin chain synthesis but do not function by a classical feedback inhibition mechanism. Since the presence of native subunits prolonged the activity of the cell-free system rather than increasing the rate of chain synthesis, the effects may be mediated secondarily by interaction with preformed monomer and dimer units or other components in the system. In contrast to the effects of native hemoglobin subunits, denatured α and β globin, but not denatured hemoglobin or other nonglobin proteins, decreased the rate of synthesis of both α and β globin chains of hemoglobin. This effect may potentiate the genetically defective rate of protein synthesis in the thalassemia syndromes.