Hydrogen-oxidizing capabilities of Helicobacter hepaticus and in vivo availability of the substrate

Hydrogen-oxidizing hydrogenase activity was detected in Helicobacter hepaticus and compared to the activity in Helicobacter pylori for characteristics associated with hydrogen uptake respiratory hydrogenases. Intact whole cells could couple H-2 oxidation to oxygen uptake, and no H-2 uptake was observed without oxygen available to complete the respiratory pathway. The H. hepaticus enzyme coupled H-2 oxidation to reduction of many positive potential acceptors, and it underwent anaerobic or reductive activation. H. hepaticus had a strong affinity for molecular H-2 (apparent K-m of 2.5 muM), and microellectrode measurements on the livers of live mice demonstrated that H-2 is available in the host tissue at levels 20-fold greater than the apparent whole-cell K-m value.