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The activity of the molybdenum hydroxylase, aldehyde oxidase, was determined in crude homogenates and (NH4)2SO4 fractions prepared from guinea pig liver, lung, kidney, intestine, spleen and heart. Xanthine oxidase was also measured in (NH4)2SO4 fractions. In each case, xanthine oxidase levels were lower than those of aldehyde oxidase; activity of the latter enzyme was highest in the liver, whereas xanthine oxidase was predominant in the small intestine. There was no significant difference in the activity of either molybdenum hydroxylase between tissues taken from male and female guinea pigs.

The metabolism of carbazeran has been investigated in vitro using liver cytosol from dog, baboon and man. Carbazeran was not metabolized in cytosol prepared from dog liver but was rapidly metabolized to a single product in baboon- and human-liver cytosol. The product was identified as 4-hydroxy carbazeran. The enzyme responsible for the 4-hydroxylation of carbazeran in vitro was shown by the use of inhibitors to be liver aldehyde oxidase. Species differences in the metabolism of carbazeran in vitro correlate well with studies in vivo; these showed that following an oral dose to man and baboon, the compound was almost completely cleared via pre-systemic 4-hydroxylation, whereas in the dog, this metabolic route appeared unimportant.