In vitro oxidation of aldehyde oxidase from rabbit liver: Specificity toward endogenous substrates

The endogenous vitamins such as pyridoxal (vitamin B6) and all-trans retinaldehyde (vitamin A) are metabolized to more or less toxic metabolites by drug-metabolizing enzymes including aldehyde oxidase (AO; EC 1.2.3.1). To better understand this function, the specificity of the rabbit liver aldehyde oxidase enzyme toward endogenous vitamins was quantitatively studied. Therefore, the present study showed the kinetic parameters of AO for the oxidation of vitamin B6 and vitamin A were measured in partially purified rabbit liver fraction. Km values of AO endogenous vitamin were observed with pyridoxal (21 ± 6.4 μM) and all-trans-retinal (46 ± 9.1 μM) respectively for partially purified rabbit liver fraction. AO from rabbit liver fraction showed high Vmax with vitamin B6 and vitamin A (1.84 ± 0.2 and 1.28 ± 0.1 nmol/min/mg protein, respectively). Therefore, the present study showed the kinetic parameters of AO for the oxidation of vitamin B6 and vitamin A were measured in partially purified rabbit liver fraction. A high affinity and low Km values of AO endogenous vitamin were observed with pyridoxal (21 ± 6.4 μM) and all-trans-retinal (46 ± 9.1 μM), respectively for partially purified rabbit liver fraction. Pyridoxal and all-trans-retinal oxidized to their metabolites (25.2 ± 12.7 and 13.3 ± 4.1 nmol/min/mg protein, respectively) by partially purified rabbit liver aldehyde oxidase. These results confirmed that the hydrophobicity enhances affinity of pyridoxal and all-trans-retinal (aromatic aldehyde) toward AO as excellent substrates. It is concluded these results presented serve as a guide for predicting the susceptibility of endogenous to oxidation by rabbit liver AO.