Adenylosuccinase Activity in Human and Rabbit Erythrocyte Lysates

Abstract

Abstract Adenylosuccinase activity was demonstrated in lysates prepared from mature human and rabbit erythrocytes by investigating both reactions catalyzed by the enzyme. The conversion of adenylosuccinate to adenosine 5'-phosphate was observed spectrophotometrically. The conversion of N-(5-amino-1-ribosyl-4-imidazolecarbonyl)-l-aspartic acid 5'-phosphate to 5-amino-1-ribosyl-4-imidazolecarboxamide 5'-phosphate was studied by measuring the incorporation of sodium (14C)-formate into the hypoxanthine of inosine 5'-phosphate when lysates were incubated with N-(5-amino-1-ribosyl-4-imidazolecarbonyl)-l-aspartic acid 5'-phosphate. The presence of adenylosuccinase in the erythrocytes of both species suggests that the human erythrocyte, which cannot effect significant conversion of inosine 5'-phosphate to adenosine 5'-phosphate, lacks adenylosuccinate synthetase activity, an enzymatic capacity possessed by the rabbit erythrocyte. The data also suggest that the inability of the erythrocytes of both species to synthesize the purine ring by the de novo pathway results from the loss of one or more steps prior to the formation of N-(5-amino-1-ribosyl-4-imidazolecarbonyl)-l-aspartic acid 5'-phosphate.