Effects of carrier morphology and buffer diffusion on the expression of enzymatic activity

A very stable esterase (EC 3.1.1.-), which hydrolyses ethyl acetate, cephalosporin C and other acetyl esters with a maximum turnover number of 3-10(2) s-1, was isolated from Bacillus subtilis ATCC 6633 and immobilized on two supports: controlled-pore glass and powdered brick, a representative of carriers having a wide pore-size distribution. Carrier morphology determines diffusion rates and the expression of activity. Rate-limiting mass transfer of buffer leads to apparent losses of activity, gross distortions of molecular pH vs. activity profiles and to apparent deviations from Michaelis-Menten kinetics.