The association of lysozyme with casein

The association of hen eggs' lysozyme with caseins was studied by using three casein substrates: (I) solutions of the various caseins, (II) artificially made casein micelles of various compositions and (III) caseins adsorbed onto soya-oil emulsion droplets. In solution, lysozyme associated most strongly with alpha(s)-casein, less with beta-casein and not with kappa-casein. Accordingly, lysozyme associated less with casein micelles composed of beta- and kappa-casein (ratio 1:2) than with whole casein micelles, which contain alpha(s)-casein as well. The extent of association with emulsified caseins was in the order alpha(s) > beta > kappa, although the differences were not large. The effects of temperature and pH on the association appeared to be small. After association with caseins, lysozyme was always found to be active, suggesting that the active site of the molecule was not involved in the association. The association of lysozyme with casein-stabilized oil droplets may provide a satisfactory technique for immobilization of the enzyme on a liquid carrier, since in situ activity is retained. (C) 1998 Elsevier Science Ltd. All rights reserved.