Activities of mitochondrial
enzymes in blood cells from 69 patients with primary
sideroblastic anemia were determined to elucidate the pathogenesis of the disease. In erythroblasts of patients with primary acquired type the activities of both
delta-aminolevulinic acid synthetase and mitochondrial
serine protease were inevitably decreased. The susceptibility to the
protease of apo-
delta-aminolevulinic acid synthetase prepared from erythroblasts of patients with this type was within the normal range, in contrast to that of
pyridoxine-responsive
anemia. The activities of mitochondrial
enzymes such as
cytochrome oxidase,
serine protease, and
oligomycin-sensitive ATPase, except
citrate synthetase, were usually decreased in mature granulocytes of the patients. Patients with hereditary
sideroblastic anemia also had decreased
delta-aminolevulinic acid synthetase activity in erythroblasts, and decreased
serine protease activity in both erythroblasts and mature granulocytes. Mature granulocytes obtained from patients with
pyridoxine-responsive
anemia before
therapy had decreased
cytochrome oxidase activity, however, the activity increased to a normal level when the patients were in remission. The activities of other mitochondrial
enzymes in mature granulocytes were within normal range in these patients before
pyridoxine therapy. The activities of these mitochondrial
enzymes in lymphocytes were within normal range in all groups of patients with primary
sideroblastic anemia. We suggest that patients with primary acquired, and possibly also those with hereditary
sideroblastic anemia have impaired mitochondrial function in both erythroblasts and granulocytes. That only
anemia is observed in these patients is because a functional abnormality of mitochondria in erythroblasts is most important because of the role of mitochondria in the formation of
heme in erythrocyte development. In contrast to these two types of
sideroblastic anemia, only
delta-aminolevulinic acid synthetase in both erythroblasts and granulocytes seems to be impaired in patients with
pyridoxine-responsive
anemia.