Effects of lysosomal collagenolytic enzymes, anti-inflammatory drugs and other substances on some properties of insoluble collagen.

1. An enzyme system present in a rat liver lysosome-rich fraction was found to liberate soluble hydroxyproline-containing products from insoluble collagen, with maximum activity at pH3.45. It was concluded that a form of cathepsin D was involved since synthetic substrates specific for trypsin were not hydrolysed. Collagenolysis was enhanced by thiol compounds and inhibited by Cu(2+) ions and the anti-inflammatory drugs phenylbutazone and ibufenac. 2. The possibility that behaviour of collagen and collagenolysis were modified by various substances, either by destruction of intramolecular and intermolecular bonds in tropocollagen or by electrostatic interactions, is discussed. Insoluble collagen was found to bind electrostatically to chondromucoprotein. This interaction was inhibited by some anti-inflammatory drugs. 3. Possible roles of the lysosomal collagenolytic enzyme system in experimental lathyrism in rats given penicillamine, and in erosion of cartilage in rheumatoid arthritis, are considered. 4. Collagenolysis in vivo, which may depend on complex interrelationships between collagen, chondromucoprotein and metal ions, is discussed in relation to possible effects, both harmful and beneficial, of anti-inflammatory drugs used in rheumatoid arthritis.