KINETIC MODELING OF OMEGA-TRANSAMINATION FOR ENZYMATIC KINETIC RESOLUTION OF ALPHA-METHYLBENZYLAMINE

A kinetic model for omega-transaminase from Bacillus thuringiensis JS6 4 was developed by using the King-Altman method to simulate the kineti c resolution of alpha-methylbenzylamine (alpha-MBA). Starting from a p ing-pong bi-bi mechanism, a complete kinetic model including substrate inhibition only in the reverse reaction (i.e., transamination between acetophenone and L-alanine) was developed. The asymmetric synthesis o f (S)-alpha-MBA proved to be difficult due to a much lower maximum rev erse reaction rate than the maximum forward reaction rate, thermodynam ically exergonic forward reaction (i.e., transamination between (S)-al pha-MBA and pyruvate), and the severe product and substrate inhibition of the reverse reaction. Experimental values for kinetic parameters s how that the product inhibition constant of (S)-alpha-MBA is the most important parameter on determining the resolution reaction rate, sugge sting that the resolution reaction rate will be very low unless (S)-al pha-MBA strongly inhibits the reverse reaction. Using the kinetic mode l, the kinetic resolution of alpha-MBA in aqueous buffer was simulated , and the simulation results showed a high degree of consistency with experimental data over a range of reaction conditions. Various simulat ion results suggest that the crucial bottleneck in the kinetic resolut ion of alpha-MBA lies mainly in the accumulation of acetophenone in re action media as the reaction proceeds, whereas L-alanine exerts a litt le inhibitory effect on the reaction. The model predicts that removing acetophenone produced during the reaction can enhance the reaction ra te dramatically. Indeed, the biphasic reaction system is capable of ex tracting acetophenone from the aqueous phase, showing a much higher re action rate compared to a monophasic reaction system. The kinetic mode l was also useful in predicting the properties of other, better enzyme s as well as the optimal concentrations of amino acceptor and enzyme i n the resolution reaction. (C) 1998 John Wiley & Sons, Inc.