Preparation and characterization of different immobilized and chemically modified preparations of lipase B from Candida antarctica: is it the activation energy a good indicator of the biocatalyst expressed activity?

Abstract

Lipase B from Candida antarctica immobilized on octyl (via interfacial activation) and octyl-vinyl sulfone (covalently attached) agarose beads via different immobilization protocols was submitted to amination and/or glutaraldehyde modifications. The catalytic performance of the resulting biocatalysts significantly varied across different substrates: using octyl-CALB with the double modification, activity increased 3.5 fold versus triacetin and decreased by 5 % using R-methyl mandelate, while using the covalent biocatalyst, activity increase by 2.2 or 20 %, respectively. Similarly, the stability of the biocatalysts —both in absolute and relative terms— was strongly influenced by the inactivation pH and the substrate used for residual activity determination. Under the tested conditions, activity versus substrate concentration followed first-order kinetics up to the substrate solubility limit, preventing the determination of kinetic parameters such as Kcat or Km. Activation energy (Eₐ) for triacetin hydrolysis was also measured for each biocatalyst under different inactivation states. Interestingly, no consistent correlation was found between Eₐ and enzyme activity. Generally, partial inactivation of the biocatalysts increased Eₐ, although some exceptions were observed. These findings suggest that Eₐ alone does not directly correlate with enzymatic activity, highlighting the complex interplay between structural enzyme modifications, substrate used to determine the enzyme activity, and the enzyme catalytic behavior