THE METABOLISM OF THE ERYTHROCYTE: XIII. ENZYME ACTIVITY IN THE RETICULOCYTE

Abstract

The object of the study was to ascertain the changes that occur in the activity of the enzymes of the reticulocyte during its maturation to the normocyte (adult erythrocyte). Blood specimens were taken from rabbits in which a severe anemia and a pronounced reticulosis (50–90% reticulocyte count) had been produced by giving the animals subcutaneous injections of acetylphenylhydrazine. Succinic dehydrogenase, cytochrome oxidase, and DPN-ase were found to be confined to the insoluble fraction of the cells while glucose-6-phosphate dehydrogenase and pyrophosphatase were found only in the soluble fraction (stroma-free hemolyzate). Isocitric, lactic, and malic dehydrogenases, fumarase, aconitase, and hexokinase were found to be present in both fractions. The activity of fumarase, hexokinase, and pyrophosphatase is much lower in the normocyte than in the reticulocyte while that of the isocitric, lactic, and malic dehydrogenases and of DPN-ase was of the same order in both types of cell. Aliquots of blood specimens were kept at 37 °C. for 12 hr. and the activity of numerous enzymes was followed at two-hourly intervals. The enzymes which are more active in the reticulocyte undergo a diminution in activity concurrently with the decrease in the reticulocyte count. Succinic dehydrogenase, cytochrome oxidase, and aconitase are absent from the normocyte. The significance of these changes with respect to the maturation of the reticulocyte is discussed.Exposure of hemolyzates of the blood specimens to the enzyme ribonuclease, to destroy any ribonucleic acid that may be present, did not alter the activity of any of the enzymes tested. The DPN-ase of the reticulocyte, as in the normocyte, was found to be a nucleosidase which splits the linkage between nicotinamide and ribose.