A Temperature-dependent Conformational Change in ~-Amino Acid Oxidase and Its Effect on Catalysis*

~-Amino acid oxidase has been shown to have a critical temperature of 12-14’. Around this temperature it has been shown that a reversible change in protein conformation occurs; the change in enthalpy of the transition has been calculated as 78,000 cal per mole. Other parameters have also been shown to change on either side of this temperature; these include sedimentation constant, ultraviolet and visible spectra, and catalytic activity. Theoretical calculations show that with very reasonable assumptions sharp breaks in Arrhenius plots are possible. It is suggested that the numerous examples in the literature of anomalous Arrhenius plots may be due to thermally induced reversible changes in protein structure.