The kinetic resolution of (R,S) sec-butylamine with the omega-transaminase (TA) from Vibrio fluvialis JS17 was performed under reduced pressure (e.g., 150 torr) to selectively remove an inhibitory product (2-butanone). The evaporation kinetics of 2-butanone at 150 torr in the buffer solution followed the first-order rate law, and the evaporation rate constant was 2.19 1/h, and independent of pH, while the evaporation kinetics of sec-butylamine is dependent on pH. A simple mathematical model of the evaporation of sec-butylamine allowing the estimation of its concentration in the reaction media was developed. The evaporation rate constant of its free amine form and the protonated amine form were 1.00 1/h, and nearly zero, respectively. Although the optimum pH of the omega-TA activity for sec-butylamine is 9.0, the optimal pH of the enzyme reaction under reduced pressure was pH 7.0, due to the higher evaporation rate of sec-butylamine at higher pH above 7.0. Using the recombinant Escherichia coli BL21 overexpressing omega-TA, 400 mM racemic sec-butylamine was resolved successfully to 98% ee of (R)-sec-butylamine with 53% conversion at 150 torr and pH 7.0. (C) 2004 Wiley Periodicals, Inc.