The kinetics of oxygen utilization by the microaerophile Campylobacter sputorium subspecies bubulus was studied. With formate as substrate two enzyme systems were found to be responsible for electron transfer between formate and oxygen. In the case of lactate oxidation one enzyme system could account for the activity measured. One of the formate-oxidizing systems possessed a high affinity for oxygen [Km(O2) = approx. 4 microM O2]. From inhibitor studies it was concluded that a respiratory chain was involved in its activity. Respiration by this system must be responsible for proton translocation and electron transport-linked phosphorylation at formate oxidation. The other enzyme system had an extremely low affinity for oxygen [Km (O2) = approx. 1 mM O2]. It was tentatively identified as the H2O2-producing formate oxidase previously found in C. sputorum. The H2O2 production by this enzyme is implicated in an explantation of the microaerophilic nature of C. sputorum. Sensitivity of formate dehydrogenase to H2O2 was demonstrated. The influence of the formate concentration on aerobic formate oxidation was determined. The pH- and temperature dependencies of oxygen uptake with formate as substrate were examined at air-saturation and at a low dissolved oxygen tension.
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