Studies on the Proteinases of the Developing Hen's Egg.(III)

On the Nature of the Proteinase with the Optimal pH at 2.8

Abstract

The nature of the proteinase with the optimal pH at 2.8, present in yolk sac, wasinvestigated. The activity was expressed by the absorption of tyrosine at 280 mμ whichwas liberated by the enzymatic hydrolysis of casein.
This enzyme action was appreciably activated by cysteine, while it was inhibited byperiodic acid and o-iodosobenzoic acid. The inhibition by these oxidants was completelyreversed by the addition of cysteine. Of metal ions tested, Mg²⁺, Mn²⁺, Ca²⁺, or Zn²⁺exerted no effect on this proteinase activity, ferrous ion displayed great stimulative influenceupon it, while heavy metals such as Cu²⁺, Hg²⁺, and Pb²⁺ caused powerful inhibitioneven in very low concentration.
From these results, it was concluded that this enzyme, together with the proteinase withthe optimal pH at 5.8, of which nature was reported in the preceding paper, was identifiedas a cathepsin type proteinase with-SH group as one of its active centers. It was furtherdemonstrated that the proteinases from yolk sac show the same properties as those fromyolk, suggesting their common origin.