Physicochemical Studies on the Binding of Chemicals with Proteins. VII. : The Binding of Phenoxazone Compound with Lens Proteins

Abstract

Bonding between 1-hydroxy-5-oxo-5H-pyrido [3, 2-a] phenoxazine-3-carboxylic acid (catalin), a phenoxazone compound said to have the action of preventing progress of cataract, with α- and β-crystallins, the chief component of lens proteins, was studied by the equilibrium dialysis method. It was thereby found that catalin bonded with both proteins by the Langmuir-type formula. Equilibrium dialysis at various pH's indicated that in either of the proteins, constants showing the saturated amount of bonding and strength of bonding of catalin hardly changed with pH. Further experiments on equilibrium dialysis by a different method showed that the bonding of catalin with these lens proteins was not represented chiefly by the electrostatic bonding between the carboxyl group in catalin molecule and the positively charged amino acid residue in the protein, but that there was a bonding whose bonding rate was larger than the dissociation rate.