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A University of Kentucky professor investigates how some of the reactions that sustain life might depend on the interactions of a few electrons.
by Kathleen Ricker The chemical reactions that make up metabolism are accelerated and controlled by catalysts known as enzymes. Composed mostly of protein, enzymes also often contain a cofactor. The cofactor can be made of metal ions, such as iron, or can be a vitamin derivative, such as a flavin (a derivative of riboflavin, also known as vitamin B2). The flavin may accelerate a reaction by brokering electron transfers between reagents to convert them to product. For example, flavins are crucial for metabolism of fatty acids. Flavin enzymes allow a kind of "controlled burn," in which the fatty acids are oxidized, allowing the energy released to be captured for use by the body. "Flavin enzymes play many crucial roles in human metabolism," says Anne-Frances Miller, associate professor of chemistry and biochemistry at the University of Kentucky. "Deficiency with regard to one of the flavoenzymes essential for fatty acid metabolism has been implicated as a possible cause of sudden infant death syndrome." It is their versatility that makes flavins especially interesting to biochemists like Miller. "Although many different enzymes contain flavins, and as a class, they do a wide variety of chemistry," says Miller, "a given enzyme catalyzes a unique reaction. So, somehow or other, the flavin cofactor is being used for different purposes in different contexts." Two types of flavin cofactors are most common: flavin mononucleotides (FMN) and flavin adenine dinucleotides (FAD). "The flavin is rather a beautiful molecule," says Miller. "It's an intense, brilliant yellow. The optical properties are yet another reflection of the very versatile electronic properties of the flavin ring." This versatility makes it both important and challenging to understand the flavin's exact mechanism and reactivity. How the mechanism and reactivity are determined by active sites--the protein environments in which a given chemical reaction occurs--is also critical. Different enzymes may apply the same flavin to different types of reactions, and, according to Miller, the interaction between the flavin and a given protein may be correlated with the resulting chemistry. Access Online | Posted 4-20-2004 |
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The enzyme nitroreductase, the focus of Miller's study. 
The ribbon diagram of the structure of the nitroreductase, showing the folding of the protein chain. |
