Isolation and characterization of cathepsin B from rabbit testis

Area of Science:

• Biochemistry
• Enzymology
• Proteolysis

Background:

• Cathepsin B (EC 3.4.22.1) is a cysteine protease implicated in various physiological and pathological processes.
• Understanding the specific characteristics of cathepsin B from different tissues is crucial for elucidating its diverse roles.

Purpose of the Study:

• To purify and characterize rabbit testicular cathepsin B.
• To investigate its enzymatic properties, substrate specificity, and the presence of endogenous inhibitors.

Main Methods:

• Purification using ion-exchange chromatography (DE-52), affinity chromatography (organomercurial agarose), and gel filtration (Sephadex G-75).
• Enzyme activity assays with varying pH, temperature, and substrate concentrations.
• Identification of an endogenous inhibitor from rabbit testes.

Main Results:

• Cathepsin B was purified to homogeneity, consisting of a single polypeptide of Mr 23,000.
• Optimal activity was observed at pH 6.0 and 43°C, requiring 2 mM cysteine.
• The enzyme demonstrated higher sensitivity towards Z-Arg-Arg-beta-naphthylamide compared to Z-Arg-beta-naphthylamide and hydrolyzed intact proteins.
• An endogenous inhibitor from rabbit testes was found to inhibit the purified enzyme.

Conclusions:

• Rabbit testicular cathepsin B is a cysteine protease with specific biochemical properties and substrate preferences.
• The presence of an endogenous inhibitor suggests a regulatory mechanism for cathepsin B activity in rabbit testes.
• These findings contribute to the understanding of testicular proteolysis and enzyme regulation.