Discussion
Which of the following is the most suitable mode to study protein conformational changes and to probe the location of active sites and coenzymes in fluorescence spectroscopy ?
Answer: C
The key gives intrinsic fluorescence.
What could and could not be confirmed: searches confirmed that the intrinsic fluorescence of a protein, mainly its tryptophan residues (excitation near 280 nm, emission near 350 nm), changes in wavelength and intensity with the local environment, and so is the standard label-free way to follow conformational changes. They did not turn up a source that ties the phrase 'location of active sites and coenzymes' to intrinsic fluorescence rather than to extrinsic probes, so that half of the keyed answer rests on the University's key.
Intrinsic fluorescence needs no added dye, and a ligand or coenzyme bound near a tryptophan quenches or shifts its emission, which is how it can report on the neighbourhood of an active site. Quenching and quantum yield are measurements or processes within a fluorescence study, not a mode. Extrinsic fluorescence, which uses an attached probe, is the usual alternative and is the option a reader might defend; the key is the University's.
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