Indoluble collagen II. The use of fluorescein labelled polymeric collagen fibrils in a very sensitive assay procedure for enzymes degrading insoluble collagen.

98% of the collagen in mature connective tissue is in the form of insoluble collagen fibers, consisting of bundles of polymeric collagen (PC) fibrils. The enzymes concerned in connective tissue remodeling degrade PC rather than tropocollagen (TC). TC is the most usual substrate for collagenase assays, and we believe it is essential to employ PC in any study of the activity of collagenolytic enzymes. In order to facilitate the study of enzymic degradation of PC we have labelled PC with fluorescein iso-thiocyanate to produce F-PC fibrils, containing 5 fluorescein labelled epilson-NH2 groups of lysine per TC molecule within the PC. The fluorescent F-PC is degraded at the same rate as PC with the release of hydroxyprolyl peptides but has the great advantage that the solubilised F-peptides can be quantitated by their fluorescent emission. The technique is described in detail employing bacterial collagenase and mammalian collagenase preparations to illustrate the methodology. The advantages of the fluorescent technique over the collagenolytic assay methods currently in use are outlined.