초록
<P><B>Abstract</B></P> <P>Hydrogen (H<SUB>2</SUB>)-producing hydrogenase (Hyd) activity of <I>E. coli</I> wild type and mutants with defects in subunits of Hyd-3 or Hyd-4 during fermentation at different glucose concentrations and pHs was studied. Hyd-3 was mainly responsible for H<SUB>2</SUB> production but a significant contribution by Hyd-4 to total H<SUB>2</SUB> production depended on the glucose concentration and pH. Surprisingly, not all Hyd-3 or Hyd-4 subunits contributed towards H<SUB>2</SUB> production. Hyd-4 mainly exhibited H<SUB>2</SUB>-oxidizing activity in cells growing on 0.2% glucose at pH 7.5, while at pH 5.5 it had a significant impact on H<SUB>2</SUB> production. Importantly, a <I>hyfG</I> mutant (lacking the large subunit of Hyd-4) had a ~2.2 fold decrease in H<SUB>2</SUB> production when cells were grown with 0.2% glucose. A similar role of Hyd-4 was shown at pH 6.5 grown with 0.8% glucose. This study provides new information to allow improvements in H<SUB>2</SUB> production yield and in our general understanding of H<SUB>2</SUB> metabolism.</P> <P><B>Highlights</B></P> <P> <UL> <LI> At pH 7.5 Hyd-4 is working towards H<SUB>2</SUB> oxidation and proton translocation. </LI> <LI> In <I>hyfG</I> mutant H<SUB>2</SUB> production at pH 5.5 was decreased ~2 fold. </LI> <LI> Hyd-3 and Hyd-4 work towards H<SUB>2</SUB> production at pH 5.5 </LI> <LI> Hyd-3 and Hyd-4 several subunits might interact forming big hydrogenase complex. </LI> </UL> </P>