Studies on the interaction of metal ions with pyruvate kinase from Ehrlich ascites-tumour cells and from rabbit muscle.

1. Pyruvate kinase (ATP-pyruvate phosphotransferase, EC 2.7.1.40) from Ehrlich ascites-tumour cells was purified approximately fivefold by chromatography on DEAE-cellulose. The enzyme was shown to have an absolute requirement for one univalent and for one bivalent metal ion. 2. The univalent metal ion requirements were satisfied by K(+), Rb(+) or NH(4) (+); Na(+) and Cs(+) were weak activators but Li(+) was inactive. 3. Ca(2+) exhibited ;non-competitive' and ;apparent competitive' effects in relation to the K(+) activation. 4. The bivalent metal ion requirements were satisfied by Mg(2+), Mn(2+) or Co(2+); Ba(2+), Sr(2+), Ca(2+), Ni(2+), Be(2+) and Cu(2+) were inactive. Mn(2+) and Co(2+) were better activators than Mg(2+). 5. The bivalent metal ion requirements of purified pyruvate kinase from rabbit muscle were satisfied by Mg(2+), Mn(2+), Co(2+) and to a smaller extent by Ni(2+). Mn(2+) and Co(2+) were better activators than Mg(2+). 6. Ca(2+) competitively inhibited the activation by Mg(2+), Mn(2+) and Co(2+) for both the tumour and rabbit enzymes. 7. It is concluded that there are no significant differences in metal ion specificity between the tumour and rabbit enzymes. 8. The possible role of metal ions in regulating enzymic and metabolic activities is considered further.