Formation and properties of horseradish peroxidase colloidal clusters

Hydrophobic modification of horseradish peroxidase by fatty acid esters (C₈, C₁₂, C₁₆, C₁₈) of N-hydroxysuccinimide was carried out. The degree of modification increases with an increase in the ester:enzyme molar ratio and reaches a maximal value of four modified amino groups when this ratio is 150:1. Covalent attachment of hydrophobic groups to the peroxidase molecules leads to a spontaneous formation of micelle-like colloidal clusters, which have a mean diameter of 65 nm at the maximal degree of modification by C₁₆-ester. The fraction of the enzyme molecules which forms clusters depends on both the length of the attached hydrophobic chain and the degree of modification. The colloidal clusters, which are composed of the modified peroxidase, have about 80 and 50% lower enzymatic activities for C₁₂- and C₁₆-modified enzymes.