Letter: Haem deficiency and chain synthesis

Globin chain synthesis ratios in sideroblastic anaemia

Globin synthesis ratios were measured on reticulocytes from nine patients with primary acquired sideroblastic anaemia (SA), four patients with hereditary or congenital SA, two patients with secondary acquired SA and three patients with iron deficiency (ID). Ten of the samples from patients with SA and all the samples from patients with ID had normal ratios. Samples from three patients had significantly abnormal ratios, one from a patient with SA and acquired Hb H disease (alpha/beta 0 X 26), one from a patient with secondary acquired SA (alpha/beta 0 X 88), and one from a patient who went on to develop acute myeloblastic leukaemia (alpha/beta 1 X 36). Globin synthesis was stimulated by 100 microM haem similarly in normal, SA and ID reticulocytes. Any limitation of globin synthesis in SA and ID is therefore not easily reversible by adding haem. Inhibition of haem synthesis in nonsideroblastic reticulocytes using 4 mM isonicotinic acid hydrazide for 1 h incubation affected neither total globin synthesis nor the alpha/beta ratio. These results contradict the view that decreased haem synthesis decreases globin chain synthesis and decreases the alpha/beta globin chain synthesis ratios in human reticulocytes. Previously reported findings that haem could reverse globin chain synthesis inhibition in SA were good evidence for a primary deficiency of haem synthesis in the erythroblasts of these patients. Our inability to substantiate these findings emphasizes the need for a re-evaluation of the aetiology of sideroblastic anaemia.

Effect of transferrin absence on in vitro globin chain synthesis in reticulocytes of beta-thalassemic patients

The effect of transferrin absence on in vitro globin chain synthesis and on the alpha/beta ratio were investigated in four patients with beta-thalassemia intermedia and one heterozygote with "silent" beta-thalassemia. With one exception the lack of transferrin in the incubation medium resulted in the reduction of the globin alpha/beta ratio which paralleled a reduction in overall protein synthesis. In one patient with beta-thalassemia intermedia, however, the absence of transferrin failed to affect this ratio.

Bone marrow and peripheral blood globin chain biosynthesis in iron deficiency

Globin chain synthesis was studied in 13 iron-deficient patients. The mean whole-cell globin alpha/beta ratio in the peripheral blood of 11 patients was 1.05 +/- 0.06 which is similar to the value 0.99 +/- 0.08 obtained for 10 controls. The ratios obtained for stroma-free globin were not significantly different from those of whole cell preparations. In contrast, the alpha/beta ratio of bone marrow was 0.73 +/- 0.14 in 10 iron deficient patients, which is significantly lower than that of controls. Two other patients had decreased alpha/beta ratios in the peripheral blood, probably because of the presence of an alpha-thalassemia gene. These results demonstrate a reduced rate of synthesis of alpha chains relative to that of beta chains in the bone marrow of iron-deficient patients that is not demonstrable in the peripheral blood.

Unequal alpha and beta globin mRNA in reticulocytes of normal and mutant f/f fetal mice

Messenger RNA (mRNA) was isolated from adult as well as normal and mutant f/f fetal mouse reticulocytes by poly-U affinity chromatography. mRNA from normal adult reticulocytes directed equal synthesis of alpha and beta globin chains in wheat germ cell free translational system. mRNA from either normal or mutant f/f fetal reticulocytes directed 40% more alpha globin synthesis than beta globin synthesis. These observations are suggestive that there is significantly more alpha mRNA than beta mRNA in normal and mutant f/f fetal mouse reticulocytes.

The effect of vincristine on haemoglobin synthesis

Vincristine in a concentration of 0.5 and 4 X 10--(5) M causes a decrease of 16% and 73% respectively, in the synthesis of globin by peripheral blood reticulocytes. At the higher drug concentration alpha/beta ratio is significantly lower than the normal ratio of unity and is 0.83 +/- 0.09. These effects of vincristine are probably related to the ability of the vinca alkaloids to bind to ribosomes and their subunits.

The effects of hemin and double-stranded RNA on alpha and beta globin synthesis in reticulocyte and Krebs II ascites cell-free systems and the relationship of these effects to an initiation factor preparation

Protein synthesis in reticulocyte lysates ceases abruptly in the absence of added hemin or in the presence of double-stranded RNA. A similar effect of double-stranded RNA is observed in Krebs II ascites cell-free systems translating exogenous globin mRNA. The shut-off of protein synthesis is due to inhibition of initiation and can be prevented or reversed by addition of the initiation factor preparation M(3). Preparations of M(1), M(2), and dissociation factor are ineffective under these conditions. The effects of added hemin, M(3), and globin mRNA on the synthesis of alpha and beta globin chains have been studied in the reticulocyte and ascites cell extracts. When the concentration of M(3) is rate limiting, the synthesis of beta chains exceeds that of alpha chains. When the concentration of mRNA is rate limiting, synthesis of alpha and beta chains is more nearly equal.