Studies on the mode of action of excess of vitamin A. 2. A possible role of intracellular proteases in the degradation of cartilage matrix

Abstract

Experiments were made to find whether normal cartilage contains an enzyme that is capable of producing an effect on the matrix like that of vitamin A. Normal cartilaginous rudiments were pretreated with distilled water to disrupt the cells and their organelles and then incubated in buffer solutions of pH 1-8. Between pH 3 and 5 the metachromatic staining of the matrix was greatly reduced, half the hexosamine content was lost (mostly as polysaccharide of high molecular weight) and protein components were liberated into the buffer. Above and below pH 3-5 there was little effect on the cartilage matrix. An extract having proteolytic activity at a pH optimum of 3 has been obtained from cartilage. The proteolytic activity is located in cytoplasmic particles, from which it can be liberated by water; it is destroyed by heating at 100[degree]. It is concluded that normal chondrocytes contain an enzyme or a group of enzymes capable of producing an effect on cartilage matrix that closely resembles that produced by excess of vitamin A.