KINETICS OF IRREVERSIBLE INHIBITION OF YEAST ALCOHOL-DEHYDROGENASE DURING MODIFICATION BY 4,4'-DITHIODIPYRIDINE

The course of inactivation of yeast alcohol dehydrogenase (YADH) using 4,4'-dithiodipyridine (DSDP) has been studied in this paper. The resu lts show that the reaction mechanism between DSDP and YADH is a compet itive, complexing inhibition. The microscopic constants for the inacti vation of the free enzyme and the enzyme-substrate complex were determ ined. The presence of the substrate NAD(+) offers strong protection fo r this enzyme against inactivation by DSDP. The above results suggest that two Cys residues are essential for activity and are situated at t he active site. These essential Cys residues should be Cys-46 and Cys- 174 which are ligands to the catalytic zinc ion. Another Cys residue, which can be modified by DSDP, is non-essential for activity of the en zyme. (C) 1997 Elsevier Science B.V.