Globin synthesis in fractionated normoblasts of β thalassemia heterozygotes

Abstract

Globin chain synthesis was examined in erythroid cells of increasing maturity, fractionated from the whole bone marrow of β thalassemia heterozygotes by a density gradient centrifugation procedure. In experiments using total cell 'globulin', a gradient of α/β chain ratios was observed, increasing with erythroid cell maturation from unity in the basophilic cells up to 2.0 in reticulocytes. Gel filtration of the lysates from these marrow fractions revealed the presence of free α chains even in the most immature cells, the amount of which increased with erythroid cell age; the total α/β ratio derived from gel filtration experiments showed a gradient similar to that observed in the total globin experiments. However, the α/β ratio of the hemoglobin fraction obtained by gel filtration remained constant throughout maturation at an average of 0.65. This latter finding is incompatible with balanced synthesis at any stage of red cell development and excludes the possibility that total β chain production is higher in the early cells than in the later cells or that α chain production in the early cells is reduced to the level of β chain synthesis. Furthermore, in a Hb S/β thalassemia marrow examined, the β(A)/β(S) ratio remained constant throughout maturation while the α/non-α ratio showed an increase like that observed in the simple β thalassemia heterozygotes. This argues strongly against increased synthesis from either the thalassemic or nonthalassemic β chain gene being responsible for the balanced synthesis in the immature cells. These findings lead the authors to suggest that, in β thalassemia heterozygotes, a large α chain pool is present throughout erythroid cell maturation and that the observed increase in α/β ratios is a function of the ability of those cells to degrade the excess α chains.