COMPARISON OF HYDROLYSIS AND ESTERIFICATION BEHAVIOR OF HUMICOLA-LANUGINOSA AND RHIZOMUCOR-MIEHEI LIPASES IN AOT-STABILIZED WATER-IN-OIL MICROEMULSIONS .2. EFFECT OF TEMPERATURE ON REACTION-KINETICS AND GENERAL-CONSIDERATIONS OF STABILITY AND PRODUCTIVITY

Humicola lanuginosa lipase (HIL) and Rhizomucor miehei lipase (RmL), i solated from commercial preparations of Lipolase and Lipozyme, respect ively, were solubilized in AOT-stabilized water-in-oil (w/o) microemul sions in n-heptane and aspects of their hydrolysis and condensation ac tivity examined. The temperature dependence of HIL hydrolysis activity in unbuffered R = 10 microemulsions matched very closely that for tri butyrin hydrolysis by Lipolase in an aqueous emulsion assay. Apparent activation energies were measured as 13 +/- 2 and 15 +/- 2 kJ mol(-1), respectively. Condensation activity, however, was essentially indepen dent of temperature over the range 5 degrees to 37 degrees C. The stab ility of HIL over a 30-day period was very good at all pH levels (6.1, 7.2, 9.3) and R values studied (5, 7.5, 10, 20), except when high pi-i s and low R values were combined. The excellent stability was reflecte d by the linearity of the productivity profiles which facilitate syste m optimization. The temperature dependence of RmL hydrolysis activity toward pNPC(4) showed a maximum at 40 degrees C and an apparent E(act) = 20 +/- 2 kJ mol(-1) was calculated based on the linear region of th e profile (5 degrees to 40 degrees C). RmL esterification activity sho wed only a slight dependence on temperature over the studied range (0 degrees to 40 degrees C) and an apparent E(act) = 5 +/- 1 kJ mol -1 wa s measured for octyl decanoate synthesis. Both RmL and HIL, therefore, have potential for application in low temperature biotransformations in microemulsion-based media. The stability of RmL over a 30-day perio d was good in R = 7.5 and R = 10 microemulsions containing pH 6.1 buff er, and this was reflected in the linearity of their respective produc tivity profiles. RmL stability was markedly poorer at more alkaline pH , however, and proved to be sensitive to relatively small changes in t he R value. (C) 1995 John Wiley & Sons, Inc.