β-ethoxyacrolein contamination increases malondialdehyde inhibition of milk xanthine oxidase activity

beta-Ethoxyacrolein (BEA), a side product that forms during the preparation of malondialdehyde (MDA) by acidic hydrolysis of tetraethoxpropane (TEP), has been found to be an inhibitor of milk xanthine oxidase (XO) several times more potent than pure MDA (NaMDA). The incubation of XO with 10 mu M BEA abolished 50% of the enzyme activity within 1 min; the inhibited enzyme was totally regenerated by dialysis and filtration through Sephadex. The BEA inhibition mode of the enzyme was mixed-type with the apparent inhibition constants (K-i) of 2.3 x 10(-6) M. An HPLC method for quantitation of BEA in the crude commonly used MDA preparation was set up. (C) 1998 Elsevier Science Inc.