Coupled spectrofluorometric assay for aminoglycoside phosphotransferases

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Aminoglycoside phosphotransferases (APHs) are enzymes that confer antibiotic resistance.
• Accurate kinetic measurements are essential for understanding APH activity and developing novel antimicrobial strategies.
• Existing spectrophotometric assays have limitations in sensitivity and accuracy for low substrate concentrations.

Purpose of the Study:

• To develop a novel, highly sensitive assay for kinetic measurements of aminoglycoside phosphotransferase substrates.
• To overcome the limitations of current spectrophotometric assays for determining enzyme kinetics.
• To accurately characterize the kinetic parameters of APH enzymes, particularly for low substrate affinities.

Main Methods:

• Adaptation of a coupled spectrophotometric assay for use in a spectrofluorometer.
• Utilizing the fluorescent properties of NADH at specific excitation and emission wavelengths (340 nm excitation, 450 nm emission).
• Measurement of kinetic constants (Km) for various aminoglycosides (amikacin, kanamycin, ribostamycin) and ATP with APH enzymes.

Main Results:

• The developed spectrofluorometric assay can accurately measure differences as small as 0.25 microM.
• Redetermined Km values for APH(3')-II with amikacin, kanamycin, and ribostamycin were found to be lower than previously reported.
• Characterization of a novel APH from a clinical isolate revealed very low Km values (approx. 1 microM) for amikacin and kanamycin.

Conclusions:

• The spectrofluorometric assay is well-suited for accurate determination of kinetic constants for APH enzymes, especially those with low Km substrates.
• This improved assay facilitates a deeper understanding of aminoglycoside resistance mechanisms.
• The findings support the development of more effective strategies to combat antibiotic resistance.