Formation and energy transfer of a fluorescent derivative of B. stearothermophilus glyceraldehyde-3-phosphate dehydrogenase.

The active site carboxymethylated glyceraldehyde-3-phosphate dehydrogenase from B. stearothermophilus when irradiated with ultraviolet light in the presence of NAD gives rise to a fluorescent derivative closely similar to that obtained from the muscle enzyme in fluorescence properties. A radiationless energy transfer also occurs between the tryptophan residues of the enzyme protein and the new fluorophore, as for the muscle enzyme. Quantitative determinations of the quantum yields and calculations according to the Förster equation five a distance of 26.36 A between the tryptophan residues and the new fluorophore. In contrast to the muscle enzyme, the irradiated thermophilic enzyme contains four fluorescent NAD derivatives per enzyme tetramer as shown by phosphorus analysis.