Quantitative study of the binding of cysteine proteinases to basement membranes.

Binding of cysteine proteinases of the papain superfamily (papain and cathepsins B, B-like and L) to basement membranes was studied by using the enzymatic activity of these proteinases against their specific fluorogenic substrates. Papain inactivated by E64 was used for Kd determination by competition experiments. The binding was characterized using the following parameters, the equilibrium constant, Kd, and the number of substrate sites, n, values of which were in the range of 10(-7) M and 10(12), respectively. Such results would be of significant interest for the understanding of the biological role of cysteine proteinases in tumour invasion and other types of tissue remodeling.