The Stability of Dimeric D-amino Acid Oxidase from Porcine Kidney Strongly Depends on the Buffer Nature and Concentration

The first step of the inactivation enzyme D-amino acid oxidase (DAAO) from porcine kidney at pH 5 and 7 is subunit dissociation, while FAD dissociation has not a relevant role. At 9, both phenomena affect stability. A strong effect buffer nature concentration on stability was found, mainly 9 (it possible same temperature to have fully inactivated in mM Hepes maintaining 100% glycine). depended buffer: 5, acetate had no clear effect, Tris, glycine (at 7) carbonate 9) decreased when increasing their concentrations; phosphate opposite effect. presence 250 NaCl usually increased stability, but this did occur all cases. effects were more significant using low concentrations DAAO reverted upon adding exogenous FAD. However, an immobilized biocatalyst which presented subunits attached support, where possible, almost disappeared. This suggested that buffers somehow altering association/dissociation equilibrium enzyme.