Gossypol is biosynthesized by the free radical coupling of two molecules of hemigossypol to yield two optically active enantiomers, (+)-gossypol and (-)-gossypol. We have demonstrated that the preferential (+)-gossypol formation in moco cotton is mediated by a (+)-gossypol-forming dirigent protein which controls the stereospecificity of peroxidative coupling of two molecules of hemigossypol by a peroxidase. Stereospecific coupling of high energy free radicals is a poorly understood process. The purification and characterization of the (+)-gossypol-forming dirigent protein will further elucidate this important process.

Purification of the moco cotton (+)-gossypol-forming dirigent protein is accomplished by anion exchange, gel filtration and affinity column chromatography. The properties of the purified dirigent protein are also characterized.