Metalloenzyme inhibitor from kidney beans: partial purification and characterization

Inhibitory activity directed against metalloenzymes has been highly purified from extracts of red kidney beans (Phaseolus vulgaris.) The inhibitor is a substance of small molecular weight and appears to be a chelator of Zn2+. One milligram of the preparation inhibited 23 milligrams carboxypeptidase A. The inhibitor also strongly inhibited carboxypeptidase B and alkaline phosphatase and could activate phosphoglucomutase that had previously been inactivated with Zn2+. The isoelectric point of the inhibitor is 4.7. The inhibitor activity was abolished by preincubation with Zn2+,Ni2+, Co2+, or Cu2+. The mechanism of inhibition of carboxypeptidases and alkaline phosphatase by the bean inhibitor is apparently due to the complexing and complete removal of Zn2+ from the enzymes.