title: The effect of alpha-tocopherol on the oxidative cleavage of beta-carotene.
abstract: Two cleavage pathways of beta-carotene have been proposed, one by central cleavage and the other by random (excentric) cleavage. The central cleavage pathway involves the metabolism of beta-carotene at the central double bond (15, 15') to produce retinal by beta-carotene 15, 15'-dioxygenase (E.C.888990988). The random cleavage of beta-carotene produces beta-apo-carotenoids, but the mechanism is not clear. To understand the various mechanisms of beta-carotene cleavage, beta-carotene was incubated with the intestinal postmitochondrial fractions of 10-week-old male rats for 1 h, and cleavage products of beta-carotene were analyzed using reverse-phase, high-performance liquid chromatography (HPLC). We also studied the effects of alpha-tocopherol and NAD(+)/NADH on beta-carotene cleavage. In addition to beta-carotene, we used retinal and beta-apo-14'-carotenoic acid as substrates in these incubations. Beta-apo-14'-carotenoic acid is the two-carbon longer homologue of retinoic acid. In the presence of alpha-tocopherol, beta-carotene was converted exclusively to retinal, whereas in the absence of alpha-tocopherol, both retinal and beta-apo-carotenoids were formed. Retinoic acid was produced from both retinal and beta-apo-14'-carotenoic acid incubations only in the presence of NAD(+). Our data suggest that in the presence of an antioxidant such as alpha-tocopherol, beta-carotene is converted exclusively to retinal by central cleavage. In the absence of an antioxidant, beta-carotene is cleaved randomly by enzyme-related radicals to produce beta-apo-carotenoids, and these beta-apo-carotenoids can be oxidized further to retinoic acid via retinal.
authors.affiliation: United States Department of Agriculture, Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA. kyeum@hnrc.tufts.edu
authors.forename: K J
authors.initials: KJ
authors.lastname: Yeum
authors.forename: A L
authors.initials: AL
authors.lastname: dos Anjos Ferreira
authors.forename: D
authors.initials: D
authors.lastname: Smith
authors.forename: N I
authors.initials: NI
authors.lastname: Krinsky
authors.forename: R M
authors.initials: RM
authors.lastname: Russell
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004041:Dietary Fats / Q000494:pharmacology; D004042:Dietary Fats, Unsaturated / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism; D014810:Vitamin E / Q000494:pharmacology*; D019207:beta Carotene / Q000378:metabolism*; D050559:beta-Carotene 15,15'-Monooxygenase
chemical_list: C493357:Bco1 protein, rat; D004041:Dietary Fats; D004042:Dietary Fats, Unsaturated; D019207:beta Carotene; D009243:NAD; D014810:Vitamin E; D010105:Oxygenases; D050559:beta-Carotene 15,15'-Monooxygenase