Jean M. Howe

Prenyltransferase from Gossypium hirsutum

Abstract A protein fraction has been purified from Gossypium hirsutum var. Coker 413 which synthesized all four geometrical isomers of farnesyl pyrophosphate from isopentenyl pyrophosphate alone, from isopentenyl pyrophosphate and geranyl or neryl pyrophosphate. Electrophoretic analysis showed that this protein fraction consisted of three proteins. One of these proteins contained isopentenyl pyrophosphate /ag dimethylallyl pyrophosphate isomerase activity. The other two proteins were insufficiently pure to characterize. Estimation of molecular weights by electrophoresis of the three proteins revealed values in the order of 3 × 10 4 to 1.3 × 10 5 . However the same protein fraction eluted as one peak from Sepharose 6B molecular sieve columns, indicative of a larger protein component as could be accounted for by the electrophoretic molecular weight estimation. From these results and from the different products synthesized it is proposed that isopentenyl pyrophosphate /ag dimethylallyl pyrophosphate isomerase and prenyltransferase (farnesyl pyrophosphate synthetase) exists as a multiprotein complex in G. hirsutum .

Biosynthesis of Gossypol

Gossypol, a yellow, phenolic compound is found in specific pigment glands distributed throughout plants belonging to the generaGossypium(cotton),Cienfuegosia,ThespesiaandKokia 18. Its structure has been elucidated by Adamset al.1as 1,1’,6,6’, 7,7’-hexahydroxyl- 3,3’-dimethyl-5,5’-diisopropyl-2,2’-binaphthyl- 8,8’-dialdehyde. Increased attention started to focus on gossypol as a result of the finding that it was responsible for the toxicity of raw cottonseed meal to monogastric animals3. For example pigs fed cottonseed meal diets containing gossypol will accumulate gossypol in most organs25, in a bound form. In view of the well known interaction of gossypol with proteins, more specifically the e-NH2 group of lysine19, it seems possible that bound gossypol is actually a gossypol-protein complex. Furthermore, the binding of gossypol to proteins28could account for the loss of the nutritional protein quality of cottonseed meal upon heating and exposure to alkaline conditions during solvent extraction of gossypol from raw cottonseed meal, to render cottonseed flower nontoxic for human consumption.