Dynamics and Geometry in Dimeric Flavoproteins from Fluorescence Relaxation Spectroscopy

The biologically widespread group of flavoproteins have in common that they contain the yellow flavin molecule as prosthetic group. The most common natural flavins are flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) which have both riboflavin as their biological precursor. To the biological chemist the most interesting feature of this versatile molecule is its redox properties which can be modulated by the (protein) environment. The redox active part of the natural flavins is the isoalloxazinic ring which can exist in the oxidized, one-electron reduced and two-electron reduced state. The redox potentials of the two one-electron steps vary greatly among different flavoproteins and depend on the chemical nature of the active site in which the isoalloxazine resides. This property makes flavin suitable as an electron shuttle in very different chemical (redox) reactions which explains its widespread occurrence in nature [1].