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Comparative fluorescence properties of lipoxygenases.
Summary
Fluorescence above 600 nm in lipoxygenases likely indicates aromatic amino acids at the catalytic site. Linoleic acid binding to soybean lipoxygenase causes significant fluorescence quenching, revealing binding kinetics.
Area of Science:
- Biochemistry
- Enzymology
- Spectroscopy
Background:
- Lipoxygenases are enzymes involved in various biological processes.
- These enzymes contain aromatic amino acids like tyrosine (Tyr) and tryptophan (Trp).
- Intrinsic fluorescence properties of enzymes can provide insights into their structure and function.
Purpose of the Study:
- To investigate the origin and significance of a specific fluorescence band in lipoxygenases.
- To explore the relationship between enzyme-ligand interactions and fluorescence changes.
- To characterize the catalytic site of lipoxygenases using fluorescence spectroscopy.
Main Methods:
- Purification of lipoxygenases from tomato, rat liver, and soybean.
- Fluorescence spectroscopy to measure emission bands.
- Inhibition studies using dithizone.
- Ligand binding assays with linoleic acid and fluorescence quenching measurements.
Main Results:
- Lipoxygenases exhibit a fluorescence band centered at 648 nm, attributed to Tyr and Trp residues.
- This fluorescence is a minor component (0.7–1.0%) of the major intrinsic fluorescence (λmax = 343 nm).
- Dithizone partially quenched the 648 nm fluorescence, and linoleic acid caused 79% quenching in soybean lipoxygenase, yielding an apparent Kd of 34 ± 3 μM.
Conclusions:
- The fluorescence above 600 nm suggests the presence of aromatic amino acids near or at the catalytic center of lipoxygenases.
- Fluorescence quenching by linoleic acid provides a method to study substrate binding and enzyme kinetics.
- This spectral characteristic may serve as a useful probe for investigating lipoxygenase structure-activity relationships.