Résumé:
A study was carried out on two acid proteases extracted from the flowers of two local plants
belonging to the family of Asteracea (Onopordum acanthium and Galactites tomentosa).
Proteases were purified in two steps, fractional precipitation with AS and molecular sifting
chromatography. The yields activity recovered are 29,78% and 23,09%, with purification
degrees of 26,65 and 15,47 for Onopordum acanthium and Galactites tomentosa respectively.
The separation of acid proteases by SDS-PAGE and zymogram show a single enzyme activity
band corresponding to a molecular weight equal to 45 kDa for both enzymes. The study of
physicochemical properties allows to obtain an optimum pH of 4, an optimum temperature of
40°C. These enzymes are inhibited by pepstatin A indicating that it is aspartylprotease and
activated by Ca + 2 ions. The Michaelis representation of the activity of two proteases gave a
form of hyperbolic curves characteristics of a monomeric structure of enzymes result
confirmed by the zymogram. The values of the kinetic parameters calculated from the
Lineweaver-Burk representation are Vmax 1329 U and 523.83 U and KM of 2.34 g /l and 3.47
g /l for Onopordum acanthium and Galactites tomentosa respectively. These enzymes caused
coagulation of milk. The coagulant activity of these proteases is optimum at 60 ° C and pH 5,
at a concentration of 50 mM in calcium. The electrophoretic profiles and HPLC show that
these coagulases have the ability to hydrolyze , and casein. These results indicate that
these enzymes can be used as substitutes for rennet or used in combination with other rennet..
