Studies on Cobaloxime Compounds. III. Effects of Various Cobaloximes as Vitamin B12 Models and of Substrate Analogs on Diol Dehydratase System

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Abstract
Various types of cobaloximes with the general formula [CoX(DH)2B] or [RCo(DH)2B] (X: CI, CN. R: alkyl groups such as methyl, ethyl, n-propyl, or i-propyl. DH: dimethylglyoximato monoanion. B: bases such as water, pyridine, nicotinamide, γ-picoline, p-toluidine, or imidazole) and some amide compounds were examined for the inhibitory effect or coenzyme activity in propanediol dehydratase of Aerobacter aerogenes. None of them act as coenzyme nor inhibitor, except for cyanoaquocobaloxime, which shows only a weak inhibitory effect that has been proved to be non-competitive. Water-soluble polymeric cobaloximes with the general formula [Co(OH) (DH)2(Copoly–AM-VPy)] (Copoly–AM-VPy: a low molecular weight copolymer of acrylamide and 4-vinylpyridine) were also prepared and examined in the enzymatic system whose inhibitory effects were very small. Other cobaloximes with the general formula [RCo(DH)2(py)] (R: β-hydroxy-n-propyl, β-hydroxy-i-propyl, or β,γ-dihydroxy-n-propyl. py: pyridine) which were three of the possible intermediate models in propanediol dehydratase system, also showed little effect on the enzymatic reaction. Substrate anologs such as 2-bromo-1-propanol, 1-bromo-2-propanol, and glycerol α-monochlorohydrin, which are considered to interact with a nucleophilic Co(I) species, presumably a component of the active site in the holoenzyme, were found to serve as substrate.