DIFFERENTIAL INACTIVATION OF ALCOHOL-DEHYDROGENASE ISOENZYMES IN ZYMOMONAS-MOBILIS BY OXYGEN

Zymomonas mobilis is endowed with two isoenzymes of fermentative alcoh ol dehydrogenase, a zinc containing enzyme (ADH I) and an iron-contain ing enzyme (ADH II). The activity of ADH I remains fully conserved, wh ile ADH II activity decays when anaerobic cultures are shifted to aero biosis. This differential response depends on the metal present on eac h isoenzyme, since pure preparations of ADH I are resistant to oxidati ve inactivation and preparations of zinc-containing ADH II, obtained b y incubation of pure ADH II with ZnCl2, showed no modification of the target for oxidative damage (His(277) containing peptide), It was cons istently found that the activity of the zinc-containing ADH II, once s ubmitted to oxidative treatment, was fully restored when iron was rein troduced into the enzyme structure, These results indicate that zinc b ound to these proteins plays an important role in the protection of th eir active centers against oxidative damage and mag have relevant bioc hemical and physiological consequences in this species.