The specificity of xanthine oxidase

Abstract

A DETAILED study of the question of identity of xanthine oxidase and the Schardinger enzyme was made in 1935 [Booth]. Most of the existing evidence infavour was confirmed while that against was shown either to have another explanation or to be insufficiently controlled. In addition several new lines ofevidence were presented. The results of the investigation pointed strongly to identity though the hypothesis could not be regarded as rigidly proved. Sincethen other authors [Basu & Mukherjee, 1936; Dixon & Keilin, 1936; Lemberg et al. 1936; Michlin et al. 1936] have extended certain of the earlier evidence, eachconcluding in favour of identity. There remain however certain points in the literature against this view. An investigation of most of these is reported in thispaper and yields no support for the separate enzyme theory. Considering the mass of evidence from the work of several authors there can be no doubt thatxanthine oxidase activates aldehydes. Nothing short of preparation of each enzyme completely free of the other can be taken as proof of non-identity. Theapparent suppression of one enzyme by an inhibitor is insufficient.