Abstract
Deoxycholate and other bile steroids activate rat liver alcohol dehydrogenase (alcohol: NAD + oxidoreductase, EC 1.1.1.1). The kinetic changes following the enzyme modification by deoxycholate were studied in both directions of the reaction ethanol + NAD + ⇌ acetaldehyde + NADH using a purified enzyme preparation. Initial rate measurements and analysis of product inhibition patterns show a particularly significant increase of the Michaelis and inhibition constants for ethanol and acetaldehyde, and also an overall change of the reaction mechanism. The kinetic pattern of the unmodified enzyme is consistent with a mechanism of the Theorell-Chance type, with kinetically irrelevant ternary complexes. The modification by 1 m m deoxycholate causes a transition toward a quite different reaction sequence. Data are inconsistent with a simple ordered mechanism and make evident the existence of a more complicated mechanism, which may include conformational changes of the binary complexes and partial randomization.
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