Peroxidase activity of horse liver alcohol dehydrogenase in the presence of β-NAD+ and hydrogen peroxide

Horse liver alcohol dehydrogenase (LADH) has been extensively studied, mainly with respect to its catalytic ability to interconvert alcohols to aldehydes, but its main physiological function appears to be still unknown, since ethanol is not formed in the animal’s body. During the last twenty years, other alternative activities have been found for LADH; the first, cronologically speaking, concerns the dismutation reaction of aldehydes [ 1,2] . An isomerase activity of LADH, concerning the isomerization of several aldehydes to ketones, was found first by Van Eys [3] and later allosterically correlated with the dehydrogenase activity [4] . In 1963 Waksman and Roberts [S] described a transaminase activity for yeast alcohol dehydrogenase and other dehydrogenases. A steroid activity of LADH, discovered in 1960 [6] , could be solely ascribed to the more basic subfraction of the enzyme preparation only in 1966 [7] and later associated to an isoenzyme of LADH [8]. It has also been found that vitamin A is oxidized to retinene by LADH in the retina [9a,9b] and more recently that methanol can function as substrate [lo]. In this paper we report evidence for a peroxidase activity of LADH, which originates when hydrogen peroxide is added to a solution containing /3-NAD’ and LADH.