DIRECT EXTRACTION OF GELATINASES FROM RAT BONE

Many studies have shown that gelatinases are secreted into the medium of cultures of various cell and tissue types, including bone cells. It is not clear however, to what extent the culture process is responsib le for inducing the expression of these proteases. In the present stud y, gelatinolytic enzymes were extracted directly from bone and other t issues and identified as bands of activity on SDS-PAGE enzymograms usi ng gelatin as the substrate. Two forms of gelatinase (72-kDa and 92-kD a) were present in extracts of normal young rat bone. Yields were mark edly higher from compact bone than from other tissues (blood, marrow, tendon, cancellous bone, articular cartilage, and skin). More 92-kDa t han 72-kDa gelatinase was extracted from bone. The proteolytic specifi city of the 92-kDa gelatinase isolated from the bone extract was shown to be similar to that reported for the enzyme isolated from tissue cu lture media. Native type I collagen was not cleaved but heat denatured type I collagen (gelatin) and native type IV, type V, type IX and typ e XI collagens were degraded. The proteolytic activity was inhibited b y EDTA. The results indicate that more gelatinases can be extracted fr om bone tissue than from other tissues using mild extraction condition s. The cellular origin and function of these enzymes in bone remain to be defined.