Change of pyruvate kinase isozymes from M2- to L-type during development of the red cell

The relationship between erythroid cell maturation and the change of pyruvate kinase (PK) isozymes was studied using fluorescent antibody techniques. The fluorescence of M2-type PK was strongest in the proerythroblast stage, and then steeply declined with red cell maturation so that only weak fluorescence was seen in orthochromatic erythroblasts. On the other hand, the fluorescence of L-type PK was seen throughout the maturation of the erythroblasts, with stronger fluorescence in the basophilic or polychromatic erythroblasts than in proerythroblasts.