Formic dehydrogenase of Bacterium coli: its inactivation by oxygen and its protection in the bacterial cell

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Abstract
Material obtained by grinding Bact. coli in the Booth-Green mill was investigated for formic dehydrogenase activity: the enzyme resided on the solid part of this material. Digestion of this sediment with trypsin gave a specific formic dehydrogenase prep. unable to react with O2. The enzyme was inhibited by high concs. of cyanide, did not require coenzyme I or II and was shown spectro-scopically to react with O2 through cytochrome b. Autol-ysis of sediment yielded a prep. which oxidized formate with O2 but was quickly inactivated. Inactivation occurred when dehydrogenase was incubated aerobically with formate and was not due to production of oxalic acid, H.CHO or H2O2. Inactivated enzyme was reactivated by anaerobic incubation: reactivation was accelerated by presence of formate. Inactivation was accelerated by increasing O2 tension; it was abolished if O2 tension was sufficiently low; accelerated by action of cyanide on carrier system (cytochrome) ; and checked by addition of MB. Digested material reacted with O2 in presence of MB but the extent of the oxidation depended upon (a) conc. of dye (b) O2 tension. The enzyme probably reacted with O2 by 2 paths: either directly leading to inactivation of dehydrogenase activity, or indirectly through carrier systems. A reconstruction of the complete system was obtained with a high cone, of cytochrome c, cytochrome oxidase and 4% O2. Increased O2 tension during growth led to inhibition of formic dehydrogenase formation.

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