Inhibition of Rhizomucor miehei and Candida rugosa lipases by d-glucose in esterification between l-alanine and d-glucose

A detailed kinetic study of the esterification of d-glucose with l-alanine catalyzed by lipases from Rhizomucor miehei (RML) and Candida rugosa (CRL) showed that both lipases follow the Ping-Pong Bi-Bi mechanism, in which l-alanine and d-glucose bind in subsequent steps releasing water and l-alanyl-d-glucose, with competitive substrate inhibition by d-glucose at higher concentrations leading to the formation of dead-end lipase·d-glucose complexes. An attempt to obtain the best fit of this kinetic model through curve fitting yielded good approximates of the apparent values of four important kinetic parameters: for RML-kcat=0.29±0.028×10−3 M h−1 mg−1, Km l-alanine= 4.9±0.51×10−3 M, Km d-glucose=0.21±0.018×10−3 M, and Ki d-glucose=1.76±0.19×10−3 M; for CRL-kcat= 0.75±0.08×10−3 M h−1 mg−1, Km l-alanine=56.2±5.7×10−3 M, Km d-glucose=16.2±1.8×10−3 M, and Ki d-glucose =21.0±1.9×10−3 M.