{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,4]],"date-time":"2026-03-04T07:07:50Z","timestamp":1772608070943,"version":"3.50.1"},"reference-count":30,"publisher":"Proceedings of the National Academy of Sciences","issue":"5","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[2001,2,27]]},"abstract":"<jats:p>\n            Carotenoids in the photosynthetic membranes of plants typically\n contain two \u03b2-rings (e.g., \u03b2-carotene and zeaxanthin) or one \u025b-\n and one \u03b2-ring (e.g., lutein). Carotenoids with two \u025b-rings are\n uncommon. We reported earlier that the\n            <jats:italic>Arabidopsis\n thaliana<\/jats:italic>\n            lycopene \u025b-cyclase (LCYe) adds one \u025b-ring to the\n symmetrical linear substrate lycopene, whereas the structurally related\n lycopene \u03b2-cyclase (LCYb) adds two \u03b2-rings. Here we describe a cDNA\n encoding LCYe in romaine lettuce (\n            <jats:italic>Lactuca sativa<\/jats:italic>\n            var.\n romaine), one of the few plant species known to accumulate substantial\n quantities of a carotenoid with two \u025b-rings: lactucaxanthin. The\n product of the lettuce cDNA, similar in sequence to the\n            <jats:italic>Arabidopsis<\/jats:italic>\n            LCYe (77% amino acid identity), efficiently\n converted lycopene into the bicyclic \u025b-carotene in a heterologous\n            <jats:italic>Escherichia coli<\/jats:italic>\n            system. Regions of the lettuce and\n            <jats:italic>Arabidopsis<\/jats:italic>\n            \u025b-cyclases involved in the determination\n of ring number were mapped by analysis of chimeric \u025b-cyclases\n constructed by using an inverse PCR approach. A single amino acid was\n found to act as a molecular switch: lettuce LCYe mutant H457L added\n only one \u025b-ring to lycopene, whereas the complementary\n            <jats:italic>Arabidopsis<\/jats:italic>\n            LCYe mutant, L448H, added two \u025b-rings. An\n R residue in this position also yields a bi-\u025b-cyclase for both the\n lettuce and\n            <jats:italic>Arabidopsis<\/jats:italic>\n            enzymes. Construction and\n analysis of chimera of related enzymes with differing catalytic\n activities provide an informative approach that may be of particular\n utility for studying membrane-associated enzymes that cannot easily be\n crystallized or modeled to existing crystal structures.\n          <\/jats:p>","DOI":"10.1073\/pnas.051618398","type":"journal-article","created":{"date-parts":[[2002,7,26]],"date-time":"2002-07-26T14:45:09Z","timestamp":1027694709000},"page":"2905-2910","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":193,"title":["One ring or two? Determination of ring number in carotenoids by lycopene \u025b-cyclases"],"prefix":"10.1073","volume":"98","author":[{"suffix":"Jr.","given":"Francis X.","family":"Cunningham","sequence":"first","affiliation":[{"name":"Department of Cell Biology and Molecular Genetics, Microbiology\r Building, University of Maryland, College Park, MD 20742"}]},{"given":"Elisabeth","family":"Gantt","sequence":"additional","affiliation":[{"name":"Department of Cell Biology and Molecular Genetics, Microbiology\r Building, University of Maryland, College Park, MD 20742"}]}],"member":"341","published-online":{"date-parts":[[2001,2,20]]},"reference":[{"key":"e_1_3_4_1_2","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1007\/978-94-009-5860-9","volume-title":"The Biochemistry of the Carotenoids","author":"Goodwin T W","year":"1980","unstructured":"T W Goodwin The Biochemistry of the Carotenoids (Chapman & Hall, 2nd Ed., London) 2, 377 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