title: zeta-Carotene cis isomers as products and substrates in the plant poly-cis carotenoid biosynthetic pathway to lycopene.
abstract: The plant carotenoid biosynthetic pathway to cyclic carotenes proceeds via carotene precursors in cis configuration. Involvement of individual isomers was elucidated by genetic complementation of desaturations and in vitro reactions of the corresponding enzyme. Determination of substrate and product specificity of phytoene and zeta-carotene desaturase revealed that 15-cis-phytoene is converted to 9,15,9'-tricis-zeta-carotene with 15,9'-dicis-phytofluene as intermediate by the first desaturase. Prior to a subsequent conversion by zeta-carotene desaturase, the 15-cis double bond of 9,15,9'-tricis-zeta-carotene has to be (photo)isomerized to all-trans. Then, the resulting 9,9'-dicis-zeta-carotene is utilized by zeta-carotene desaturase via 7,9,9'-tricis-neurosporene to 7,9,7',9'-tetracis-lycopene. Other zeta-carotene isomers that are assumed to be spontaneous isomerization products were not converted, except for the asymmetric 9-cis-zeta-carotene. This isomer is desaturated only to 7,9-dicis-neurosporene resembling a dead-end of the pathway. Prolycopene, the product of the desaturation reactions, is finally isomerized by a specific isomerase to all-trans-lycopene, which is a prerequisite for cyclization to beta-carotene. The 5-cis-lycopene and the 9-cis-and 13-cis-beta-carotene isomers detected in leaves are thought to originate independently from cis precursors by non-enzymatic isomerization of their all-trans forms.
authors.affiliation: Biosynthesis Group, Department of Botany 213, J.W. Goethe University, P.O. Box 111932, 60054 Frankfurt, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Breitenbach
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
mesh_terms: D002212:Capsicum / Q000201:enzymology; D002338:Carotenoids / Q000096:biosynthesis* / Q000737:chemistry* / Q000378:metabolism; D005638:Fruit / Q000201:enzymology; D007536:Isomerism; D000077276:Lycopene; D018551:Solanum lycopersicum / Q000201:enzymology; D015394:Molecular Structure; D010088:Oxidoreductases / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology; D013379:Substrate Specificity; D019207:beta Carotene / Q000378:metabolism; D024321:zeta Carotene / Q000737:chemistry / Q000378:metabolism
chemical_list: D024321:zeta Carotene; D019207:beta Carotene; D002338:Carotenoids; C008604:neurosporene; C003140:phytofluene; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; C099215:zeta-carotene desaturase; D000077276:Lycopene