Collagenolytic Cathepsins of Rabbit Spleen: A Kinetic Analysis of Collagen Degradation and Inhibition by Chicken Cystatin

We have investigated the steady state kinetics of the degradation of native fibrillar collagen at pH 3.4 by four collagenolytic cathepsins of rabbit spleen. For each enzyme, the dependence of initial velocity on collagen concentration was well described by the Michaelis-Menten mechanism. K_m, expressed as the concentration of triple-helical chains, and k_cat values were determined for cathepsins B, L, N and S. The ratio of K_cat to K_m suggest that cathepsins L and N are far more effective at collagen solubilization than either cathepsins S or B. K; values were determined for the inhibition of collagenolytic activity at pH 3.4 using cystatin, a naturally-occurring cysteine proteinase inhibitor. All four cysteine proteinases were inhibited by cystatin in this assay system, although it was found to be a tighter binding inhibitor of cathepsin L, than for cathepsins N and S (approximately 5-fold less), or cathepsin B (approximately 500-fold less).