PROBING STRUCTURE-ACTIVITY RELATIONSHIP IN DIAMINE OXIDASE - REACTIVITIES OF LYSINE AND ARGININE RESIDUES

Lysine and arginine residues of pig kidney diamine oxidase (DAO) were modified with 2,4,6-trinitrobenzenesulphonic acid (TNBS), 2,3-butanedi one and phenylglyoxal, respectively, using different concentrations an d time periods. Lysine residues are classified into 3 categories: comp letely exposed, highly reactive; sluggish, partly buried; and unreacti ve, completely buried. About 21 lysine residues whose modification did not lead to any significant conformational change as well as loss of catalytic activity are believed to be less important for the structura l stability of the enzyme. On the other hand, the remaining 19 lysine residues are more important in maintaining the native structure of the enzyme as evidenced by the change in hydrodynamic parameters and loss of catalytic activity upon their modification. Arginine residues when probed with butanedione or phenylglyoxal treatment resulted in the si gnificant loss of catalytic activity without any change in conformatio n implicating their involvement in the catalytic function of the enzym e. Significant change in conformation was noted when 10 arginine resid ues were modified, which suggests the structural role of these residue s.