Cysteine proteinase inhibitors of the canine intervertebral disc

Several species of cysteine proteinase inhibitors have been demonstrated in the greyhound intervertebral disk which were resolved four species (M_r 15 8000, 16 600, 17 200 and 17 800) by gelatin-SDS-polyacrylamide gel electrophoresis. Reductive alkylation did not affect their inhibitory capability not their electrophoretic migration on gelatin-SDS-polyacrylamide gel electrophoresis. The cysteine proteinase inhibitors from the nucleus pulposus and annulus fibrosus were identical as assessed by the aforementioned criteria, although the level in the nucleus was found to be higher than that in the annulus. Ion-exchange chromatography demonstrated distinct acidic and basic forms of the disc cysteine proteinase inhibitor. The latter species was the most abundant and its M_r was determined to be 16 900 by gelatin-SDS-polyacrylamide gel electrophoresis. Both forms were shown to be strongly inhibitory against the cysteine proteinases. papain and ficin, but were less strongly inhibitory against cathepsin B (EC 3.4.22.1). Presumably these disc cysteine proteinase finhibitors play a regulatory role in the metabolism of proteoglycans and collagen by endogenous cysteine proteinases.