Solvent condition in triolein hydrolysis by Rhizopus delemar lipase using an AOT reverse micellar system

Abstract

The hydrolysis of triolein catalyzed by Rhizopus delemar lipase was examined using AOT reverse micellar systems formulated with several straight-chain alkanes (C 6–C 10), isooctane, and cyclohexane as non-polar organic solvents. The highest initial reaction rate was obtained in the isooctane system. In the straight-chain systems, the initial reaction rate was correlated with the hydrophobicity of the solvent, log P, but not with the water content ( W 0: molar ratio of water to AOT) in the micellar organic phase. In the isooctane system, the initial reaction rate was strongly dependent on W 0 and was maximal when W 0 is equal to approximately 13. Since there is known to be a linear correlation between reverse micelle size and W 0, the degree of curvature of the micellar interface also appears to influence enzyme reactivity, especially with a bulky solvent like isooctane. The percolation temperature decreased with increasing W 0 more rapidly in the isooctane system than in the other systems, indicating enhancement of the attractive interaction between reverse micelles. A Michaelis–Menten analysis showed the isooctane system to have the highest specificity ratio ( k cat/ K m). Isooctane at W 0=13 was thus considered to be the best solvent condition for triolein hydrolysis in a 50 mM AOT reverse micellar system.