The noncovalent adsorption of chloroperoxidase (CPO) from the mold Caldariomyces fumago onto a talc, a mineral support that is available in various forms in industrial quantities and low cost, was investigated at two different values of pH (3.0 and 6.0). pH was found to affect both adsorption and enzymatic activity owing to the isoelectric point of CPO (pI approximate to 4) and the chemical characteristics of the absorbing surface of the talc tested. The hydrophobic and chemically neutral talc, type 15M00, favored adsorption (up to 8 mg CPO-g(-1) talc); however, it led to strong inhibition of enzymatic activity on adsorption at pH 3, although activity was conserved (approximate to 61% for halogenation and up to 72% for oxidation) by performing the adsorption at pH 6. In contrast, the hydrophilic and slightly acidic, calcined talc, type CLST, was less favorable to adsorption (less than or equal to 2.5 mg CPO-g(-1) talc); however, the CLST-CPO combination had excellent enzymatic activity (80-126%) irrespective of the pH of adsorption and without modification of the pH optimum of the enzyme. The results were accounted for in terms of the inter actions between CPO and the talc as a function of the adsorption pH. Adsorption onto talc may thus lead to an improvement in reaction selectivity of CPO particularly in the competing halohydroxylation-oxidation reactions, thereby widening the potential industrial applications of this enzyme. (C) 1998 Elsevier Science Inc.