Location of an Essential Arginine Residue in the Primary Structure of Pig Aldose Reductase

There have been several recent advances in the elucidation of the structure and mechanism of action of aldose reductase (ALR2; EC 1.1.1.21). The enzyme exhibits ordered sequential kinetics and during the kinetic mechanism a conformational change occurs upon coenzyme binding (Grimshaw et al., 1990; Kubiseski et al., 1992). Unlike most oxidoreductases the rate limiting step is not the release of NADP+ but rather, in the forward direction at least, the rate of isomerization of the binary enzyme-coenzyme complex, E*•NADP⇄E•NADP (Kubiseski et al., 1992). Chemical modification studies previously have suggested several amino acid residues essential for the function of the enzyme e.g. lysine (Morjana et al., 1989), arginine (Halder et al., 1985) and cysteine (Liu et al., 1989). The cloning and sequencing of ALR2 from several species has enabled the precise location of such residues in the primary structure (Carper et al., 1987; Garcia-Perez et al., 1989; Nishimura et al., 1990; Schade et al., 1990). Moreover, the development of expression systems for ALR2 has allowed an examination of critical residues by site-directed mutagenesis (Bohren et al., 1991; Yamaoka et al., 1992).