Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2005
Publication Date: 1/20/2006
Citation: Benedict, C.R., Liu, J., Stipanovic, R.D. 2006. The perioxidative coupling of hemigossypol to gossypol in cottonseed extracts. Phytochemistry. 67:356-361. Interpretive Summary: Cottonseed meal contains a high quality protein that is under utilized because of the presence of a toxic compound called gossypol. Gossypol occurs naturally in the plant in two forms referred to as (+)-gossypol and (-)-gossypol in the ratio of 3:2. Only (-)-gossypol is toxic. If cottonseed could be developed that contains only (+)-gossypol it would be more widely utilized. To achieve this goal, we are studying how (+)-gossypol and (-)-gossypol are produced in the plant. We have shown that a unique chemical reaction takes place in the seed as it develops to maturity that controls this ratio. This is the first step required to identify how this reaction takes place with the goal of regulating this process to give exclusively the nontoxic (+)-gossypol.
Technical Abstract: A 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 to 94% by 1 mM 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 the embryo extracts can be accounted for by the non-enzymatic random coupling of the free radicals of hemigossypol produced by the peroxidase. In contrast, peroxidase reaction mixtures containing embryo extracts of G. hirsutum race marie-galante produced 73% (+) gossypol and 27% (-) gossypol. These data and the fact that these intact seed contain 95% (+) gossypol suggest a regio-stereoselective intramolecular 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.