Interaction of gelonin with zinc

Gelonin, a plant protein which inactivates eukaryotic ribosomes, binds to zinc chelate Sepharose from which it is eluted with EDTA or histidine. After purification by metal chelate affinity chromatography, gelonin maintains the associated zinc-dependent proteinase activity previously described. In equilibrium dialysis about 4 moles of zinc bind per mole of gelonin with a dissociation constant of 0.96 mM. Ca2+ behaves as a mixed competitive and non-competitive inhibitor of the binding of zinc with Ki = 29 mM.