The aspartyl proteinases of Penicillium caseicolum and P. roqueforti acted identically on /f-casein; both enzymes split at least 3 bonds: Lys 29 -Ile 30 , Lys 97 -Val 98 and Lys 99 -Glu 100 . From a sl -casein, these proteinases released 6 main degradation products which arose from the splitting of 4 bonds; P. roqueforti aspartyl proteinase was found to cleave 1 bond at a higher rate than P. caseicolum aspartyl proteinase. A hypothetical sequential hydrolysis mechanism of a sl -casein by these 2 enzymes is proposed from a study of the degradation by isoelectric focusing and by 2-dimensional electrophoresis.Proteinases play a fundamental role in the dairy industry. Fox (1981) distinguishes 3 proteinase classes which can be involved; these are the indigenous proteinases naturally occurring in milk (e.g. plasmin), the endogenous proteinases coming from microorganisms and the exogenous proteinases which are added to the milk (e.g. milk-clotting enzymes). The in vitro and in situ proteolytic action of some of these proteinases on caseins, particularly those of bovine pepsins A and chymosin, is now well-known (for a recent review, see Visser, 1981). However, the enzymes of microorganisms have not been studied extensively and the characterization of their proteolytic activities on casein is still ill-defined. This communication reports a comparison of the action of the aspartyl proteinases of Penicillium caseicolum and P. roqueforti on ft-and a sl -caseins as measured by isoelectric focusing (IEF) and 2-dimensional electrophoresis. In addition the 3 main bonds cleaved by P. caseicolum aspartyl proteinase on /J-casein were identified. These 2 mould enzymes, which belong to the exocellular proteolytic system (Lenoir et al. 1979;Zevaco et al. 1973) play an important role during Camembert-type cheese ripening (P. caseicolum) and blue cheese ripening (P. roqueforti). MATERIALS AND METHODS Preparation of caseins and proteinasesWhole casein, purified a sl B-and /?A 2 -caseins were prepared according to Mercier et al. (1968). P. caseicolum aspartyl proteinase (a gift from Dr Lenoir) was prepared as described elsewhere (Lenoir et al. 1979). P. roqueforti aspartyl proteinase was prepared according to Zevaco et al. (1973).

Mots clésMétalloprotéase -Penicillium caseicolum -Penici1lium roquejorti -Hydrolyse des caséines -Focalisation isoélectrique -Electrophorèse bidimensionnelle. Titre abrégéHydrolyse des caséines par les métalloprotéases de Penicillium. Summary COMPARATIVE STUDY OF THE ACTION OF METALLOPROTEINASES OF PENICILLIUM CASEICOLUM AND PENICILLIUM ROQUEFORT! ON USl-ANDB-CASEINSWe have studied and compared in vitro action of the metalloproteinases of Penicillium caseicolum and Penicillium roqueforti on purified MÉMOIRES ORIGINAUX 235Us, and [3-caseins using electrophoresis, isoelectric focusing and 2-dimensional electrophoresis. The digestion patterns observed after migration showed that these proteinases cleaved numerous peptide bonds on both caseins. From a qualitative point of view these metalloproteinases acted in a similar way on