A rationale for stabilization of oxygen-labile enzymes: application to a clostridial hydrogenase

A general procedure for stabilization of O2-labile enzymes exploiting "salting out" of oxygen from the microenvironment in the molecular layers immediately adjacent to charged surfaces of polyionic solid adsorbents has been developed. Empirical verification of this rationale is provided. The half-life of air inactivation of the O2-labile hydrogenase (EC 1.12.7.1) from Clostridium pasteurianum is increased 20- to 25-fold simply by adsorption (noncovalent binding) in dilute Tris.HCl buffer on common anion exchange supports such as DEAE-cellulose or Dowex 1-X2. Predicted increases in degree of stabilization by using more densely charged adsorbents (such as polyethyleneimine-cellulose), as well as bulkier solvent counter-anions, are found; half-lives for air inactivation for the bound hydrogenase can be increased to 3000-fold longer than that of the free enzyme. Most of the total catalytic activity, assayed as H2 evolution from dithionite mediated by methyl viologen or ferredoxin, is retained, whereas the expected suppression of H2 uptake in the reverse reaction is observed.