A neutral protease in rheumatoid synovial fluid capable of attacking the telopeptide regions of polymeric collagen fibrils.

Fluorescent-labelled polymeric collagen fibrils have been prepared which contain three fluoresein residues in the telopeptide regions and four fluorescein residues in the helical region of each tropocollagen unit within the polymer. This material has been used as a substrate for the study of enzymes present in the synovial fluid of inflamed rheumatoid joints which are capable of degrading polymeric collagen fibrils. Two enzyme systems were observed, one inhibited by EDTA and having the properties of the known synovial collagenase, the other having the properties of a neutral protease. The neutral protease was found to be present in sonicates of the polymorphonuclear leucocytes in the synovial fluids of inflamed joints. This enzyme attacked the telopeptides of fluorescein-labelled polymeric collagen fibrils and was similar to trypsin in removing two residues of fluorescein-labelled peptides per tropocollagen molecule within the polymeric collagen fibrils but did not depolymerise the polymeric collagen fibrils.