SUBSTRATE-SPECIFICITY OF ASCORBATE OXIDASE - UNEXPECTED SIMILARITY TOTHE REDUCTION SITE OF DOPAMINE BETA-MONOOXYGENASE

A series of ascorbate derivatives has been used to examine the specifi city of the reduction site of ascorbate oxidase. Replacement of the 6- OH group of ascorbic acid with either hydrogen or bromine does not alt er the substrate activity significantly. 6-Amino-6-deoxy-L ascorbic ac id is a weak substrate for the enzyme, suggesting that positively char ged groups at the 6-position are not well tolerated by the enzyme. The modification of the 5-OH reduces the effective interaction with the e nzyme and the replacement of 6-OH with 6-S-phenyl- or 6-O-phenyl group s significantly increases the affinity for the enzyme. Both 2-Amino-6- S-phenyl-L- ascorbic acid and imino-D-glucoascorbic acid are not subst rates for the enzyme. The stereoelectronic properties and alternate bi nding modes of these molecules are being considered to explain these o bservations. The substrate specificity of the enzyme is compared to th e specificity of the reduction site of dopamine beta-monooxygenase. (C ) 1994 Academic Press, Inc.