Kinetic Analysis of R-Selective ω-Transaminases for Determination of Intrinsic Kinetic Parameters and Computational...

Reliable kinetic parameters of enzymes are of paramount importance for a precise understanding of catalytic performance, which is essential for enzyme engineering and process optimization. Here, we developed a simple and convenient method to determine intrinsic kinetic parameters of R-selective ω-transaminases (ω-TAs) with a minimal set of kinetic data. Using (R)-α-methylbenzylamine ((R)-α-MBA) and pyruvate as a substrate pair, two R-selective ω-TAs from Arthrobacter sp. and Aspergillus fumigatus were subjected to kinetic measurements. In contrast to S-selective ω-TAs, both R-selective ω-TAs were observed to be devoid of substrate inhibition by pyruvate. Double reciprocal plot analysis was carried out with two sets of kinetic data obtained at varying concentrations of (R)-α-MBA under a fixed concentration of pyruvate and vice versa, leading to the determination of three intrinsic kinetic parameters, i.e., one k_cat and two K_M values, using three regression constants. The validity of the kinetic parameters was verified by a self-consistency test using a regression constant left out in the kinetic parameter determination, showing that deviations of calculated regression constants from the experimental ones were less than 15%. Because the kinetic parameters for (R)-α-MBA and pyruvate are not apparent but intrinsic, a cosubstrate substitution method enabled rapid determination of intrinsic parameters for a new substrate pair using just one set of kinetic data. Eventually, computational modeling of kinetic resolution of rac-α-MBA was carried out and showed a good agreement with experimental reaction progresses.