To further investigate the erythroid nature of the two human erythroleukemia cell lines, K562 and HEL-60, and to define the ontogeny of pyruvate kinase (PK) isozymes (R, M2) in developing human erythroid cells, we have studied the isozymic alterations, if any, during differentiation of these cell lines in vitro and normoblasts isolated from fetal liver in vivo. PK activity of erythroleukemic cell lines was intermediate between that observed in leukocytes and in fetal liver erythroblasts. These cell lines contained a high level of M2-PK, but R- PK was always present, albeit at low concentrations, in all the clones or subclones we studied. Erythroblasts from fetal liver were separated according to density on a Stractan gradient. R-PK levels were nearly constant in the different fractions, whereas M2-PK levels markedly decreased as the erythroblasts became mature and almost completely disappeared in late erythroid cells. Thus, these results clearly demonstrate the erythroid origin of these cell lines.

No abstract

Mature erythrocytes contain a specific isozyme of pyruvate kinase (R- PK) while immature erythroblasts coexpress R-PK and another isozyme, M2- PK. To determine what roles degradation and decreasing of synthesis played in the disappearance of M2-PK during erythroid maturation, M2-PK and R-PK synthesis and degradation were studied in erythroblasts from fetal liver and blood BFU-E-derived erythroblasts from healthy subjects, an erythroleukemic patient, and a patient with an erythrocyte PK hyperactivity associated with M2-PK persistence in mature erythrocytes. In normal erythroblasts, R-PK synthesis was constant throughout erythroid maturation, whereas M2-PK synthesis decreased to the point of becoming undetectable. R-PK degradation was very low, while M2-PK degradation was more pronounced and steady during erythroid maturation. In leukemic erythroblasts, total protein turnover was higher than in normal cells, but the M2-PK degradation rate was lower. In erythroblasts from the patient with M2-PK persistence in mature erythrocytes, M2-PK synthesis did not decline with cell maturation. In conclusion, our results emphasize the importance of the decrease of M2- PK synthesis in the disappearance of M2-PK during erythroid maturation. Further studies of patients with pathologic persistence of M2-PK synthesis will help in the understanding of this event involved in erythroid maturation.

No abstract

Mature erythrocytes contain a specific isozyme of pyruvate kinase (R- PK) while immature erythroblasts coexpress R-PK and another isozyme, M2- PK. To determine what roles degradation and decreasing of synthesis played in the disappearance of M2-PK during erythroid maturation, M2-PK and R-PK synthesis and degradation were studied in erythroblasts from fetal liver and blood BFU-E-derived erythroblasts from healthy subjects, an erythroleukemic patient, and a patient with an erythrocyte PK hyperactivity associated with M2-PK persistence in mature erythrocytes. In normal erythroblasts, R-PK synthesis was constant throughout erythroid maturation, whereas M2-PK synthesis decreased to the point of becoming undetectable. R-PK degradation was very low, while M2-PK degradation was more pronounced and steady during erythroid maturation. In leukemic erythroblasts, total protein turnover was higher than in normal cells, but the M2-PK degradation rate was lower. In erythroblasts from the patient with M2-PK persistence in mature erythrocytes, M2-PK synthesis did not decline with cell maturation. In conclusion, our results emphasize the importance of the decrease of M2- PK synthesis in the disappearance of M2-PK during erythroid maturation. Further studies of patients with pathologic persistence of M2-PK synthesis will help in the understanding of this event involved in erythroid maturation.