Effect of Flavin Monosulphate on Old Yellow Enzyme

Abstract

WHEN flavin mononucleotide combines with the protein of old yellow enzyme to form the holoenzyme, the fluorescence of the free mononucleotide disappears¹. This quenching of fluorescence has been attributed to bond formation between the protein and the imino NH(3) group of the flavin mononucleotide², and Weber³ has suggested that the tyrosyl hydroxyl group of the protein may be responsible. In support of this hypothesis, Nygaard and Theorell⁴ showed that 3,5 iodination of some of the tyrosyl groups resulted in a drastic change in the association and dissociation velocity constants. In addition to the binding of the imino NH(3) position, the extensive kinetic studies of Theorell and Nygaard^4–7 on the combination of old yellow enzyme apoprotein with its prosthetic group have indicated that the phosphoric acid residue of flavin mononucleotide is attached to (probably two) primary amino-groups in the protein.