The Reactivity of Flavoproteins with Sulfite

Abstract

The ability of sulfite ions to form an adduct with the flavin prosthetic group has been examined for a large number of flavoproteins.Reaction was found with glucose oxidase (l), D-and L-amino acid oxidases, oxynitrilase, lactate oxidase, and glycollate oxidase.The dissociation constant of the reversible reaction was determined under a variety of conditions.With glycollate oxidase the stoichiometry was found to be 1 mole of sulfite reacting with each equivalent of enzyme-bound fIavin.No reaction of sulfite was detected with the other flavoproteins studied, even at high concentrations of sulfite.The correlation is made that those enzymes which react readily with sulfite are those which react catalytically with oxygen as a hydrogen acceptor; no sulfite reaction was found with flavoprotein dehydrogenases.An attempt has been made to correlate various properties of flavoproteins, such as the type of flavin semiquinone they exhibit, evidence for charged groups in the vicinity of the flavin, their ability to react with sulfite, and their reactivity with oxygen and with one-electron acceptors.A possible scheme is developed which might account for the different pathways of oxygen reactivity exhibited by the flavoprotein oxidiises, dehydrogenases, and hydroxylases.III studies on the glucose osidase from *-lsperyillus niger a previously undcscribed reaction between a flavoprotein and sulfite was discovered (1).This reaction, which ~1s shown to be inckpenclent of the presence of 02 or other electron acceptors was characterized by a bleaching of the visible absorption spectrum of the enzyme, resulting in the production of a new absorption band in the vicinity of 330 ml*, with a spectrum similar to, but not identical with, that of the reduced flavoprotein.