Mechanism-based inhibition of bacterial γ-butyrobetaine hydroxylase

Article abstract of DOI:10.1021/ja00158a051

The branched-chain hydrocarbon acids 5,5-dimethylhexanoic acid and 3-(2,2-dimethylcyclopropyl)propanoic acid were examined as substrates and inhibitors of the γ-butyrobetaine hydroxylase from Pseudomonas sp. AK1, an α-ketoglutarate-dependent, non-heme iron-containing dioxygenase. The former compound is a very slow alternate substrate of the hydroxylase. It is oxygenated at carbon 3 at ca. 0.1% of the rate of hydroxylation of the natural substrate γ-butyrobetaine, but the reaction is extensively uncoupled: α-ketoglutarate decarboxylation occurs almost 6 times as frequently as carbon hydroxylation. In contrast, 3-(2,2-dimethylcyclopropyl)propanoic acid was observed to be a first-order time-dependent inactivator of the hydroxylase. Inactivation occurred only in the presence of both oxygen and α-ketoglutarate, and the natural substrate provided nearly complete protection from inactivation; thus this cyclopropane-bearing analogue must be a mechanism-based inhibitor of the enzyme.