[Pyrivate kinase deficiency. II. Biochemical studies (author's transl)]

Pyruvate kinase deficiency was studied biochemically in ten homozygous and seven heterozygous individuals who previously had been examined clinically and hematologically (see part I). In crude hemolysates some properties of the deficient enzymes were found to be altered. The pH optimum was shifted towards the alkaline range, and the thermal optimum was found between 17 and 27 degrees Cinstead of between 37 und 47 degrees C. The abnormal enzymes were much less stable than normal pyruvate Kinase (PK), and more susceptible to inhibition by adenosinetriphosphate. The affinity to adenosinediphosphate was normal in all cases whereas the affinity to phosphoenolpyruvate was either normal (two cases/, increased (two cases) or slightly decreased (six cases). Fructosediphosphate activated the abnormal enzymes by a factor of 1.5--18 and simultaneously transformed the sigmoidal affinity curve with phosphoenolpyruvate into the hyperbolic curve known for the normal enzyme. The consumption of glucose and the formation of lactate were higher in PK deficient erythrocytes than in normal cells but lower than in erythrocyte populations with similar reticulocyte counts. The formation of 2,3-diphosphoglycerate was markedly increased, whereas its breakdown was low. A close relation between the degree of reticulocytosis and the impairment of glucose metabolism was found. In patients with high reticulocyte counts, i.e. in the splenectomized patients, the highest concentrations of glucose-6-phosphate, phosphoenolpyruvate, 3-phosphoglycerate and 2,3-diphosphoglycerate as well as a high formation and a low breakdown of 2,3-diphosphoglycerate and a deficit in lactate formation were found. In heterozygotes, small increases of the concentration of glucose-6-phosphate, phosphoenolpyruvate and 3-phosphoglycerate were demonstrated. Our results support the conclusion that PK deficiency is mainly a disorder of the reticulocytes. Their metabolism grossly deteriorates within the venous sinuses of the spleen. Splenectomy improves the clinical course because this critical area of microcirculation with a highly unfavourable metabolic milieu is eliminated.