A thioamide substrate of carboxypeptidase A

Area of Science:

• Enzymology
• Biochemistry
• Protein Chemistry

Background:

• Carboxypeptidase A (CPA) is a key enzyme in protein metabolism.
• Substrate analogues are valuable tools for studying enzyme mechanisms.
• Z-Gly-Phe is a known substrate for CPA, providing a basis for comparison.

Purpose of the Study:

• To synthesize and characterize a thioamide analogue of Z-Gly-Phe.
• To investigate the inhibitory and substrate properties of Z-Glys-Phe with CPA.
• To elucidate the mechanism of CPA-catalyzed hydrolysis of the thioamide analogue.

Main Methods:

• Synthesis of carbobenzoxythioglycyl-L-phenylalanine (Z-Glys-Phe).
• Enzyme kinetics assays using a ninhydrin-based method.
• Determination of inhibition constants (Ki) and kinetic parameters (Km, kcat).

Main Results:

• Z-Glys-Phe was synthesized as a thioamide analogue of Z-Gly-Phe.
• Z-Glys-Phe exhibited weak competitive inhibition of CPA (Ki = 1.4 mM).
• The L-isomer of Z-Glys-Phe served as a substrate for CPA, with kinetic parameters (Km = 1.1 mM, kcat = 5.3 s-1) indicating lower catalytic efficiency compared to Z-Gly-Phe.
• Hydrolysis involved exclusive C-N bond cleavage.

Conclusions:

• Z-Glys-Phe is a valuable tool for probing the active site of CPA.
• The thioamide modification affects both binding and catalytic activity of CPA.
• CPA demonstrates specificity for the L-isomer and cleaves the C-N bond in the thioamide analogue.