REDUCTION OF CARBON-MONOXIDE TO FORMALDEHYDE BY THE TERMINAL OXIDASE OF THE MARINE BACTERIUM PSEUDOMONAS-NAUTICA STRAIN-617

When exposed to CO, the aerobic respiratory system of the marine bacterium Pseudomonas nautica strain 617, previously reduced with dithionite, undergoes reoxidation. When dealing with the purified oxidase (dithionite reduced) exposure of the enzyme to CO induces its reoxidation (collapse of its alpha band). Under our experimental conditions, this form of the oxidase could not be reduced again by dithionite. Addition of formaldehyde to the native oxidized enzyme resulted in full inhibition of the oxidase reduction by dithionite, presumably due to complex formation. We hypothesized a reduction of CO into formaldehyde and a locking of the active site by the reaction product. By using flash photolysis, it was possible to turn over the enzyme, accumulate the reaction product and identify it as formaldehyde. When using the membrane-bound enzyme, formaldehyde accumulated without the help of flash photolysis. This unusual reduction of CO to formaldehyde could be related to the previously reported uncommon features of the P. nautica oxidase, in particular O2 reduction into H2O2 as end product [(1989) FEBS Lett. 247, 475-479].