The peroxidative coupling of hemigossypol to (+)- and (-)-gossypol in cottonseed extracts.

Peroxidase(s) present in embryo extracts of Gossypium hirsutum cv. Texas Marker 1 catalyzed a bimolecular coupling of [4-(3)H]-hemigossypol to [4,4'-(3)H(2)]-gossypol. The reaction was dependent on the addition of H(2)O(2) and was inhibited 71-94% by 1 and 10mM sodium azide. The phenolic coupling produced 53% (+)-gossypol and 47% (-)-gossypol in close agreement to the 49% (+)-gossypol and 51% (-)-gossypol found in the intact seed. The nearly racemic mixture of (+)-and (-)-gossypol produced in these embryo extracts can be accounted for by non-enzymatic random coupling of the free radicals of hemigossypol produced by the peroxidase. In contrast, peroxidase reaction mixtures containing crude embryo extracts of G. hirsutum var. marie-galante produced 73% (+)-gossypol and 27% (-)-gossypol. These data from the marie-galante extracts and the fact that these intact seed contain 95% (+)-gossypol suggest a regio-stereoselective bimolecular coupling of hemigossypol to gossypol. The development of the peroxidative coupling of hemigossypol to gossypol in maturing seed of G. hirsutum cv. Texas Marker 1 was correlated to the formation of gossypol and suggests that peroxidative coupling of hemigossypol contributes to gossypol biosynthesis.