Specificity of a milk clotting enzyme extracted from the thistle Cynara cardunculus L. : action on oxidised insulin and K-casein

K-casein and oxidised insulin were digested with an acid protease extracted from Cynara cardunculus L. The fragments produced were isolated and characterised. In k-casein cleavage occurred specifically at Phe105-Met106 bond. In oxidised insulin seven fragments were obtained and cleavage was found to occur at the carboxylic side of (Phe, Leu, Ile)-X, where X was preferentially Val or Tyr. The results obtained with insulin B chain suggests that Cynara cardunculus L. protease possesses a greater specificity than other acid proteases reported.