Excess substrate inhibition of xanthine oxidase: a reexamination

Xanthine oxidase has long been considered to be subject to inhibition by excess substrate. It is now shown that, although such inhibition can be seen in Tris or N,N-bis(2-hydroxyethyl)glycine buffers, earlier reports in which phosphate, pyrophosphate, or Veronal buffers were used were probably the result of a spectrophotometric artifact imposed by stray light in the incident beam.