Preferential inhibition of the lycopene epsilon-cyclase by the substituted triethylamine compound MPTA in higher plants.
In addition to the usual complement of carotenoids found in the plant leaf tissues, lettuce (Lactuca sativa), unusually, possesses large amounts of the diol lactucaxanthin. This carotenoid possesses two epsilon-end-groups and its presence provides a good model in which to study the effects of the substituted triethylamine compound 2-(4-methylphenoxy)triethylamine (MPTA) on the cyclisation of beta- and epsilon-end-groups during the biosynthesis of carotenoids. Treatment with 10 or 20microM MPTA significantly reduced levels of both beta-carotene and neoxanthin (up to 18-fold), whilst levels of violaxanthin and lutein were less affected (4-fold reduction). In contrast, levels of lactucaxanthin were not reduced even at the highest inhibitor concentration, and at 10microM MPTA levels of this xanthophyll doubled. The pigment stoichiometry of the bulk light-harvesting complex (LHCIIb) isolated from treated plants shows that lactucaxanthin successfully substituted for lutein and neoxanthin in two of the xanthophyll binding sites, namely L2 and N1. Inhibition of cyclisation was accompanied by the accumulation of lycopene and trace amounts of delta-carotene and a number of oxygenated derivatives of these precursors. Two forms of mono-hydroxy lycopene were identified together with mono-epoxy delta-carotene.
Phillip
Denise M
DM
School of Biological and Earth Sciences, Liverpool John Moores University, Byrom St., Liverpool L3 3AF, UK. d.m.phillip@livjm.ac.uk
Young
Andrew J
AJ
D002338:Carotenoids / Q000096:biosynthesis*; D005021:Ethylamines / Q000494:pharmacology*; D019753:Intramolecular Lyases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D018545:Lactuca / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D031224:Raphanus / Q000187:drug effects / Q000378:metabolism; D024341:Xanthophylls / Q000096:biosynthesis; D019207:beta Carotene / Q000031:analogs & derivatives / Q000096:biosynthesis
D005021:Ethylamines; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D024341:Xanthophylls; D019207:beta Carotene; C082524:2-(4-methylphenoxy)triethylamine; D002338:Carotenoids; C005613:violaxanthin; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase; C011947:neoxanthin