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Updated: Aug 5, 2026

The Importance of Correct Protein Concentration for Kinetics and Affinity Determination in Structure-function Analysis
Published on: March 17, 2010
Interactions between ovine cathepsin L, cystatin C and alpha 2-macroglobulin. Potential role in the genital tract
S Peloille1, A Esnard, J L Dacheux
1Laboratoire d'Enzymologie et Chimie des Protéines, EP CNRS 117, Université François Rabelais, Tours, France.
Abstract:
The specific inhibitor of cysteine proteinases, cystatin C, was purified from ram rete testis fluid and the conditioned medium of Sertoli cells. This molecule associated with sheep liver cathepsin L at one of the fastest rates ever described for a proteinase/inhibitor interaction (1.75 +/- 0.20 x 10(8) M-1.s-1). But the association rate constant for the interaction of cathepsin L with alpha 2-macroglobulin, a non-specific inhibitor of proteinases, was also extremely high (8.8 +/- 0.75 x 10(6) M-1.s-1). Cathepsin L complexed with alpha 2-macroglobulin was protected from inhibition by type 2 and type 3 cystatins. The data indicate that cystatin C is the most potent inhibitor of cathepsin L in mammalian male genital tract fluids, whereas alpha 2-macroglobulin may act as a terminal acceptor of this enzyme. These inhibitors could therefore inhibit the activated form of procathepsin L which may appear during the complex process of spermatozoa production and maturation in the testis and epididymis.
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