| The enzyme uses a pyridoxal phosphate (PLP) cofactor (purple) and lysine (yellow outline) to carry out chemistry. The substrate amino acid (green) reacts with the cofactor to form an adduct (as shown in this model) which then rearranges to give product. Substrate specificity for the negatively charged aspartic acid substrate is determined by the positively charged guanidino groups of arginine 386 and arginine 292, which have no catalytic role. Mutation of arginine 292 to aspartic acid produces an enzyme that prefers arginine to aspartate as a substrate. Adapted from Cronin, C.N. and Kirsch, J.F.: Biochemistry 1988, 27:4572–4579; Almo, S.C. et al.: Prot. Eng. 1994, 7:405–412. |
