Role of disulfides in biological activity and conformational stability of pig kidney diamine oxidase: evidence for two disulfide states.

Six disulfides are found to be present in pig kidney diamine oxidase and all of these are available to reducing agents under nondenaturating conditions. Disulfide reduction with dithiothreitol followed by carbamidomethylation indicated two states of disulfides, each containing three groups, distinguishable by pH dependence. The first group of three disulfides has a functional role in catalytic activity. The another class of three disulfides showed accessibility only at higher pH values and appears to be important in maintaining the three dimensional structure of the molecule. The disulfides for these two activities appear to be independent of each other. Almost similar behaviour was noticed with copper depleted apo-enzyme.