Specific temperature dependence of diamine oxidase activity and its thermal stability in the presence of polyvinylalcohol.

An inflexion point on the dependence of the swine kidney diamine oxidase activity upon the temperature was found at 40-43 degrees C, suggesting a conformational transition. The activation energies with putrescine as substrate calculated from the Arrhenius plots were 38.23 kcal/mol for the temperature interval 25-40 degrees C and only 15.14 kcal/mol for the range 45-60 degrees C. These values suggest two different conformations, one corresponding to the interval below 40 degrees C and another one between 43-60 degrees C, with an intermediate transitory form corresponding to the inflexion point at 40-43 degrees C. For various temperature decades within 10-60 degrees C, peculiar Q10 values in the range 1.37-3.00 (differing from the usual value Q10 = 2), were obtained. The non-strictly Arrhenius curves, the activation energies and the inflexion point were quite similar with and without 0.05% polyvinylalcohol. This particular temperature effect found for swine kidney diamine oxidase is similar to the one reported for bovine serum amine oxidase. An increased enzyme thermal stability was obtained in the presence of high molecular weight polyvinylalcohol.