CHAPTER XIII - The Yellow Enzymes

Abstract

This chapter discusses the yellow enzymes. Warburg and Christian described a yellow enzyme which they obtained from brewers' yeast and called it the yellow oxidation enzyme. Kuhn and Wagner-Jauregg called the yellow substances present in various plants and animals flavins. Various flavins were described, for example, lactoflavin of milk, hepatoflavin of liver, verdo-flavin of grass, a flavin in egg white, and one in urine. The flavin of these workers was the same substance which is called today riboflavin, or sometimes, lactoflavin. In aqueous solution riboflavin is yellow and gives a green fluorescence with visible and ultraviolet light. It is reduced to the colorless dihydro compound by sodium dithionite. Riboflavin mononucleotide is the prosthetic group of the old yellow enzyme, L-amino acid oxidase of animals, and TPN-cytochrome c reductase of yeast. Flavin Adenine Dinucleotide (FAD) is the prosthetic group of all yellow enzymes except the old yellow enzyme, animal L-amino acid oxidase, and TPN-cytochrome c reductase of yeast. Synthetic yellow enzyme is prepared by adding isoalloxazine adenine dinucleotide to the protein of the old yellow enzyme. This synthetic enzyme has an absorption band at 465 mμ. It has the same catalytic properties as the old yellow enzyme. It has 78% of the activity of the old yellow enzyme in terms of its ability to transport oxygen.