ACETYLENE INHIBITION OF AZOTOBACTER-VINELANDII HYDROGENASE - ACETYLENE BINDS TIGHTLY TO THE LARGE SUBUNIT

Acetylene is a slow-binding inhibitor of the Ni- and Fe-containing dim eric hydrogenase isolated from Azotobacter vinelandii. Acetylene was r eleased from hydrogenase during the recovery from inhibition. This ind icates that no transformation of acetylene to another compound occurre d as a result of the interaction with hydrogenase. However, the releas e Of C2H2 proceeds more rapidly than the recovery of activity, which i ndicates that release of C2H2 is not sufficient for recovery of activi ty. Acetylene binds tightly to native hydrogenase; hydrogenase and rad ioactivity coelute from a gel permeation column following inhibition w ith (C2H2)-C-14. Acetylene, or a derivative, remains bound to the larg e 65 000 MW subunit (and not to the small 35 000 MW subunit) of hydrog enase following denaturation as evidenced by SDS-PAGE and fluorography of (C2H2)C-14-inhibited hydrogenase. This result suggests that C2H2, and by analogy H-2, binds to and is activated by the large subunit of this dimeric hydrogenase. Radioactivity is lost from (C2H2)-C-14-inhib ited protein during recovery. The inhibition is remarkably specific fo r C2H2: propyne, butyne, and ethylene are not inhibitors.