Fluorescence Studies on Lipoamide Dehydrogenases of Pig Heart

II. Microenvironments of Tryptophan Residues

Abstract

The tryptophan residues of two forms of pig heart lipoamide dehydrogenase (LD (I) and LD (II)) were investigated fluorometrically.
The tryptophan contents of LD (1) and LD (II) determined by the fluorescence method were 3 mol and 2 mol per mol of FAD, respectively. These values were in good agreement with those found by the MCD method.
The microenvironments of the tryptophan residues were investigated by fluo-rescence quenching titration with acrylamide. The tryptophan residues of both enzymes were in heterogeneous microenvironments, and CD spectra showed some differences between these microenvironments in the two enzymes. Energy transfer from tryptophan residues to bound FAD was equally efficient in the two enzymes.
It seems probable that the three tryptophan residues in LD (I) are all in different microenvironments, but that two of them are in microenvironments almost identical to those of the corresponding residues in LD (II).