Esterification of polyunsaturated fatty acids by various forms of immobilized lipase from Rhizomucor miehei

Ethyl esterification specificity of a lipase from Rhizomucor miehei for pol yunsaturated fatty acids (PUFA) was compared at 1 and 100 mM to study molec ular recognition of PUFA. The chemical shift of methylene adjacent to carbo xyl groups in the nuclear magnetic resonance spectrum of docosahexaenoic ac id (DHA) in ethanol moved to a lower magnetic field as the concentration of DHA increased, suggesting that the degree of dissociation of DHA decreased . Specificity constants or apparent second-order rate constants (V-max/K-m or catalytic power) for 1 mM esterification by immobilized lipases were hig her than the native lipase. Immobilized hydrophobic carrier of low mass tra nsfer resistance for the esterification substrate may improve maximal veloc ity and affinity for the substrate. Higher specificity constants for 1 mM s ubstrates were observed using immobilized lipases fixed on an anion exchang e resin with glutaraldehyde and on a cation exchange carrier with carbodiim ide. Activity yields measured with 1 mM PUFA substrate were high. For the s ubstrates at a concentration of 100 mM, higher specific constants with thes e bifunctional reagents were not observed but higher activity yields were f ound.