Isothiocyanates as substrates for human glutathione transferases: structure-activity studies

Area of Science:

• Biochemistry
• Enzymology
• Toxicology

Background:

• Human glutathione transferases (GSTs) are crucial enzymes involved in detoxification.
• Isothiocyanates, found in foods, are known substrates for GSTs.
• Understanding GST-isothiocyanate interactions is vital for metabolism and drug development.

Purpose of the Study:

• To investigate the catalytic activity of four human GST isoenzymes (A1-1, M1-1, M4-4, P1-1) against 14 isothiocyanate substrates.
• To compare the efficiency of different GSTs in conjugating isothiocyanates.
• To analyze the structure-activity relationships of isothiocyanates as GST substrates.

Main Methods:

• Enzymatic assays were performed using 14 different isothiocyanate compounds.
• Kinetic parameters, including molar absorption coefficients and rate constants, were determined.
• Comparison with previously studied 4-hydroxyalkenal substrates was conducted.

Main Results:

• All four human GSTs (A1-1, M1-1, M4-4, P1-1) catalyzed the conjugation of isothiocyanates.
• GSTs M1-1 and P1-1 exhibited the highest catalytic efficiency, whereas GST M4-4 was the least efficient.
• Isothiocyanates are rapidly conjugated by GSTs, with structural similarities to 4-hydroxyalkenals in terms of substrate stabilization.

Conclusions:

• Human GSTs effectively metabolize a range of isothiocyanates, including dietary components.
• Significant differences in catalytic efficiency exist among GST isoenzymes for isothiocyanate conjugation.
• Isothiocyanates represent a class of highly reactive GST substrates with implications for xenobiotic metabolism.