Hydroxamic acid production and active-site induced Bamberger rearrangement from the action of α-ketoglutarate dehydrogenase on 4-chloronitrosobenzene

Abstract

The α-ketoglutarate dehydrogenase complex obtained from E. coil has been found to convert 4-chloronitrosobenzene (3) into N-(4-chlorophenyl)succinohydroxamic acid (4) and N-(4-chloro-2-hydroxyphenyl)succinamic acid (5). The conversion of 4-chloronitrosobenzene (3) into these two products is not quantitative and attempts to identify other, significant low-molecular-weight metabolites have been unsuccessful. Partial enzyme-inactivation has been observed during the incubation of 4-chloronitrosobenzene (3) with α-ketoglutarate dehydrogenase. The direct enzymic conversion of the hydroxamic acid (4) into the isomeric product (5) did not occur. These results are interpreted on the basis of a mechanism in which N-(4-chlorophenyl)hydroxylamine (6) is generated at the enzyme active-site by a redox process. Condensation of the active-site bound products would give rise to the hydroxamic acid (4) directly, while a Bamberger-like rearrangement of the active-site bound hydroxylamine (6), followed by condensation of the resulting o-aminophenol, would explain the production of the succinamic acid (5).