The biosynthesis of rubber from β-hydroxy-β-methylglutaryl-coenzyme A in Hevea brasiliensis latex

Abstract

1. beta-Hydroxy-beta-methyl[3-(14)C]glutaryl-CoA is efficiently incorporated into rubber on incubation with Hevea brasiliensis latex, and the incorporation is diminished in the presence of unlabelled mevalonate. beta-Hydroxy-beta-methylglutaric acid is not utilized for rubber synthesis, but inhibits the formation of rubber from beta-hydroxy-beta-methylglutaryl-CoA. 2. The incorporation of beta-hydroxy-beta-methylglutaryl-CoA into rubber is stimulated equally by NADP(+) and NADPH and less so by NAD(+) and NADH. ATP is slightly stimulatory and CoA is inhibitory. 3. beta-Hydroxy-beta-methylglutaryl-CoA reductase is concentrated in the sediment (bottom fraction) formed by centrifuging latex at low speed and the enzyme is unstable in the absence of cysteine or GSH. The formation of NADPH takes place in the latex serum. 4. There is a marked seasonal variation in the extent of beta-hydroxy-beta-methylglutaryl-CoA incorporation into rubber in latex, but mevalonate incorporation is relatively constant. This observation, together with the finding that beta-hydroxy-beta-methylglutaryl-CoA reduction is the rate-limiting step in the formation of rubber from beta-hydroxy-beta-methylglutaryl-CoA, suggests that the conversion of beta-hydroxy-beta-methylglutaryl-CoA into mevalonate is of importance in the regulation of rubber synthesis. 5. Evidence suggesting that beta-hydroxy-beta-methylglutaryl-CoA lyase is present in H. brasiliensis latex has been obtained.

Laticifer-Specific cis-Prenyltransferase Silencing Affects the Rubber, Triterpene, and Inulin Content of Taraxacum brevicorniculatum

“…Therefore, we investigated additional regulatory models. The MVA pathway is thought to be the main source of IPP in rubberproducing plants (Bandurski and Teas, 1957;Hepper and Audley, 1969;Sando et al, 2008), so we studied the expression of hydroxymethylglutaryl-coenzyme A reductase (HMGR), the rate-limiting enzyme of the MVA pathway (Chappell et al, 1995). This enzyme is known to be feedback regulated by isoprenoid compounds (for review, see Stermer et al, 1994).…”

“…Large quantities of isopentenyl diphosphate (IPP) are required for rubber biosynthesis, and this is thought to be derived from the mevalonate (MVA) pathway, as indicated by radioactive labeling assays using latex extracts from H. brasiliensis (Bandurski and Teas, 1957;Hepper and Audley, 1969). Enzymes in the plastid-localized methylerythritol phosphate (MEP) pathway are also expressed in H. brasiliensis latex (Seetang-Nun et al, 2008).…”

La glycéraldehyde‐3‐phosphate déshydrogénase du latex d'Hevea brasiliensis

“…I1 faut souligner enfin que la mise en hvidence de cette dbshydroghnase rhghnhrant le NADPH, au sein du latex d'Hevea brasiliensis, fait apparaitre sous un jour diffhrent le fonctionnement des enzymes oxydatives de la voie des pentoses (glucose-6-phosphate dbshydrogbnase et gluconate-6-phosphate dbshydroghnase) considbrbes jusqu'alors comme les enzymes essentielles de la production de NADPH [43] nhcessaire b la biosynthkse du caoutchouc [5,6] …”

“…Its optimum pH is around 8. 6 and it catalyses a reaction that is irreversible. Its K,-values for the substrate, NADP and NAD respectively are : 1.2 mM, 10 pM and 12 mM.…”

“…Toutefois, 1'6tude de la r6g6neration des dinucleotides de la nicotinamide, dans leur forme rbduite, problbme important en ce qui concerne le mbta- bolisme du latex puisque le NADPH est un cofacteur nhessaire & la synthbse du cispolyisoprhne [5,6], nous a permis de constater que la glycolyse dans le serum de latex pouvait Bgalement fonctionner avec du NADP.…”