Properties of milk-clotting enzyme from Aspergillus versicolor and isolation of rennin-like enzyme

Abstract

Some properties of the crude milk-clotting enzyme produced by Aspergillus versicolor in surface culture were studied. The enzyme action was optimal at pH 6 and 45°C. Addition of increasing amounts of calcium chloride at constant level of skim milk enhanced milk-clotting. The enzyme possessed a high milk-clotting activity/proteolytic activity ratio and compared well to calf rennin. Electrophoresis in 0·01 m acetate buffer at pH 3·42 separated the enzyme into three protein components. Two components showed only proteolytic activity while the third component showed high milk-clotting activity and feeble proteolytic action. That third component was the rennin-like enzyme fraction, which showed 2·8-fold purification. The rennin-like enzyme fraction was activated 5-fold by treatment with either maleic or iodoacetic acid. It was partially inhibited by reduced glutathione and parachloromercuribenzoate, and completely inhibited by iodine and potassium cyanide.