Isolation and characterization of a basic carboxypeptidase from human seminal plasma

Area of Science:

• Biochemistry
• Enzymology
• Reproductive Biology

Background:

• Carboxypeptidases are enzymes that remove C-terminal amino acids from peptides.
• Seminal plasma contains various enzymes, but their specific roles in reproductive function are not fully elucidated.
• Understanding seminal plasma enzymes is crucial for reproductive health research.

Purpose of the Study:

• To purify and characterize a novel carboxypeptidase from human seminal plasma.
• To investigate the enzyme's substrate specificity and kinetic properties.
• To explore the potential physiological roles of this enzyme in reproduction.

Main Methods:

• Purification using gel filtration (Sephacryl S-300) and affinity chromatography (arginine-Sepharose).
• Enzyme activity assays with various peptide and ester substrates.
• Molecular weight determination by gel filtration and SDS-PAGE.
• Characterization of pH optimum, inhibitors, and activators.
• Cross-reactivity testing with antisera against other carboxypeptidases.

Main Results:

• A carboxypeptidase cleaving C-terminal arginine or lysine was purified with a 280% activity increase.
• The enzyme exhibited a neutral pH optimum, was inhibited by o-phenanthroline, and activated by cobalt.
• Purified enzyme showed high specific activity and hydrolyzed biologically active peptides like bradykinin and enkephalins.
• It did not cross-react with antiserum to human plasma carboxypeptidase N, distinguishing it from other known carboxypeptidases.

Conclusions:

• A unique seminal plasma carboxypeptidase was isolated and characterized.
• The enzyme's properties suggest roles in regulating peptide hormone activity and protein degradation during semen liquefaction.
• Further research is warranted to confirm its precise functions in fertility and reproductive processes.