The peroxidative coupling of hemigossypol to (+)- and (-)-gossypol in cottonseed extracts
2006
Benedict, C.R. | Liu, J. | Stipanovic, R.D.
Peroxidase(s) present in embryo extracts of Gossypium hirsutum cv. Texas Marker 1 catalyzed a bimolecular coupling of [4-3H]-hemigossypol to [4,4'-3H2]-gossypol. The reaction was dependent on the addition of H2O2 and was inhibited 71-94% by 1 and 10 mM 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.
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