For a shy shark that spends most its time resting on the sea floor (see video above), the chain catshark certainly wears a flashy outfit. Both it and the swell shark are the only sharks known to give off a green glow when exposed to light. Now, researchers have tracked down the source of this fluorescence—and it’s nothing like they’ve seen before.Glowing jellyfish may be the most famous fluorescent sea creatures—radiating brilliant greens and blues—and scientists have used their proteins to track proteins in cells and even create glow-in-the-dark cats. On the trail of more such proteins, researchers surveying glowing fish—there are 180 known so far—focused on the chain catshark and swell shark, native to the waters off the coasts of the U.S. Northeast and Southern California, respectively.When they took a piece of skin from living sharks and extracted all of the compounds, they were surprised: The glowing compounds weren’t proteins at all, but breakdown products of an unusual form of the amino acid tryptophan. In animals, most of the tryptophan goes toward creating proteins. But some is converted to a compound called kynurenine, which in turn is a building block for niacin, a vitamin, and is involved with diabetes, inflammation, depression, and even cancer. When an atom of the element bromine tags along, this kynurenine releases a green glow when exposed to the blue light below the ocean’s surface, the team reports today in iScience.Sign up for our daily newsletterGet more great content like this delivered right to you!Country *AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, The Democratic Republic of theCook IslandsCosta RicaCote D’IvoireCroatiaCubaCuraçaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and Mcdonald IslandsHoly See (Vatican City State)HondurasHong KongHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People’s Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People’s Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, The Former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinianPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRWANDASaint Barthélemy Saint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTaiwanTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofVietnamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweI also wish to receive emails from AAAS/Science and Science advertisers, including information on products, services and special offers which may include but are not limited to news, careers information & upcoming events.Required fields are included by an asterisk(*)These sharks typically lie on the ocean bottom, waiting to ambush octopuses and other sea creatures. No one really knows why they glow, though it might help shark species tell each other apart or recognize potential mates, as males and females have different fluorescent patterns. But these compounds may also protect the sharks, as one of the glowing compounds kills bacteria. And given that these animals wallow in bacteria-laden sediments on the ocean bottom, such antibacterial properties likely come in very handy.*Correction, 28 August, 11:25 a.m.: In this story, the locations of the swell shark and chain catshark have been changed to reflect their actual home ranges. By Elizabeth PennisiAug. 8, 2019 , 11:00 AM This shark glows using a process previously unknown to science
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