{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,13]],"date-time":"2026-07-13T15:52:33Z","timestamp":1783957953637,"version":"3.55.0"},"reference-count":65,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2016,12,21]],"date-time":"2016-12-21T00:00:00Z","timestamp":1482278400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>It was in the 1950s that the term polysulfide or persulfide was introduced in biological studies. The unfamiliar term \u201csulfane sulfur\u201d sometimes appeared in papers published in the 1970s, and was defined in the review article by Westley in 1983. In the article, sulfane sulfur is described as sulfur atoms that are covalently bound only with sulfur atoms, and as this explanation was somewhat difficult to comprehend, it was not generally accepted. Thus, in the early 1990s, we redefined these sulfur species as \u201cbound sulfur\u201d, which easily converts to hydrogen sulfide on reduction with a thiol reducing agent. In other words, bound sulfur refers to a sulfur atom that exists in a zero to divalent form (0 to \u22122). The first part of this review focuses on the fluorescent derivatization HPLC method\u2014which we developed for measurement of bound sulfur\u2014and explains the distribution of bound sulfur and the hydrogen sulfide-producing ability of various tissues, as clarified by this method. Next, we discuss diverse physiological functions and involvement of polysulfide, a typical type of bound sulfur, in the redox regulation system. Additionally, we also address its possible physiological role in the central nervous system, based on its action of scavenging reactive carbonyl compounds.<\/jats:p>","DOI":"10.3390\/molecules21121753","type":"journal-article","created":{"date-parts":[[2016,12,23]],"date-time":"2016-12-23T04:09:09Z","timestamp":1482466149000},"page":"1753","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":40,"title":["Sulfur Atom in its Bound State Is a Unique Element Involved in Physiological Functions in Mammals"],"prefix":"10.3390","volume":"21","author":[{"given":"Shin","family":"Koike","sequence":"first","affiliation":[{"name":"Department of Analytical Biochemistry, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuki","family":"Ogasawara","sequence":"additional","affiliation":[{"name":"Department of Analytical Biochemistry, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2016,12,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"73","DOI":"10.1006\/abio.1993.1556","article-title":"Determination of bound sulfur in serum by gas dialysis\/high-performance liquid chromatography","volume":"215","author":"Ogasawara","year":"1993","journal-title":"Anal. Biochem."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"179","DOI":"10.1146\/annurev.nu.06.070186.001143","article-title":"Metabolism of sulfur-containing amino acids","volume":"6","author":"Stipanuk","year":"1986","journal-title":"Annu. Rev. Nutr."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1066","DOI":"10.1523\/JNEUROSCI.16-03-01066.1996","article-title":"The possible role of hydrogen sulfide as an endogenous neuromodulator","volume":"16","author":"Abe","year":"1996","journal-title":"J. Neurosci."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1016\/bs.mie.2014.11.036","article-title":"Mechanistic chemical perspective of hydrogen sulfide signaling","volume":"554","author":"Nagy","year":"2015","journal-title":"Methods Enzymol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1235","DOI":"10.1007\/s00702-016-1600-z","article-title":"Hydrogen polysulfide (H2Sn) signaling along with hydrogen sulfide (H2S) and nitric oxide (NO)","volume":"123","author":"Kimura","year":"2016","journal-title":"J. Neural Transm."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1016\/bs.mie.2014.11.020","article-title":"Real-time assays for monitoring the influence of sulfide and sulfane sulfur species on protein thiol redox states","volume":"555","author":"Greiner","year":"2015","journal-title":"Methods Enzymol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1016\/0076-6879(87)43009-7","article-title":"Sulfane sulfur","volume":"143","author":"Wood","year":"1987","journal-title":"Methods Enzymol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1359","DOI":"10.1039\/an9911601359","article-title":"Determination of trace amounts of sulphide in human red blood cells by high-performance liquid chromatography with fluorimetric detection after derivatization with p-phenylenediamine and iron (III)","volume":"116","author":"Ogasawara","year":"1991","journal-title":"Analyst"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"3000","DOI":"10.1248\/cpb.40.3000","article-title":"High performance liquid chromatographic determination of bound sulfide and sulfite and thiosulfate at their low levels in human serum by pre-column fluorescence derivatization with monobromobimane","volume":"40","author":"Togawa","year":"1992","journal-title":"Chem. Pharm. Bull."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1016\/0003-2697(91)90295-5","article-title":"Biological sulfane sulfur","volume":"67","author":"Westley","year":"1991","journal-title":"Anal. Biochem."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"394","DOI":"10.1016\/0003-2697(89)90659-3","article-title":"A sensitive gas chromatographic method for determination of protein-associated sulfur","volume":"178","author":"Hannestad","year":"1989","journal-title":"Anal. Biochem."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"31","DOI":"10.1016\/bs.mie.2014.11.039","article-title":"Measurement of H2S in vivo and in vitro by the monobromobimane method","volume":"554","author":"Shen","year":"2015","journal-title":"Methods Enzymol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"941","DOI":"10.1111\/j.1476-5381.2010.00704.x","article-title":"A monobromobimane-based assay to measure the pharmacokinetic profile of reactive sulphide species in blood","volume":"160","author":"Wintner","year":"2010","journal-title":"Br. J. Pharmacol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"14774","DOI":"10.1038\/srep14774","article-title":"Identification of H2S3 and H2S produced by 3-mercaptopyruvate sulfurtransferase in the brain","volume":"5","author":"Kimura","year":"2015","journal-title":"Sci. Rep."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1775","DOI":"10.1039\/C5MB00216H","article-title":"Persulfides: Current knowledge and challenges in chemistry and chemical biology","volume":"11","author":"Park","year":"2015","journal-title":"Mol. Biosyst."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"ra72","DOI":"10.1126\/scisignal.2000464","article-title":"H2S signals through protein S-sulfhydration","volume":"2","author":"Mustafa","year":"2009","journal-title":"Sci. Signal."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"1906","DOI":"10.1089\/ars.2012.4645","article-title":"Hydrogen sulfide protects against cellular senescence via S-sulfhydration of Keap1 and activation of Nrf2","volume":"18","author":"Yang","year":"2013","journal-title":"Antioxid. Redox Signal."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"575","DOI":"10.1002\/anie.201305876","article-title":"Detection of protein S-sulfhydration by a tag-switch technique","volume":"53","author":"Zhang","year":"2014","journal-title":"Angew. Chem. Int. Ed. Engl."},{"key":"ref_19","first-page":"1","article-title":"A novel persulfide detection method reveals protein persulfide- and polysulfide-reducing functions of thioredoxin and glutathione systems","volume":"2","author":"Pader","year":"2016","journal-title":"Sci. Adv."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"26866","DOI":"10.1074\/jbc.M115.672816","article-title":"Reaction of hydrogen sulfide with disulfide and sulfenic acid to form the strongly nucleophilic persulfide","volume":"290","author":"Cuevasanta","year":"2015","journal-title":"J. Biol. Chem."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"22457","DOI":"10.1074\/jbc.M109.010868","article-title":"Relative contributions of cystathionine \u03b2-synthase and \u03b3-cystathionase to H2S biogenesis via alternative","volume":"284","author":"Singh","year":"2009","journal-title":"J. Biol. Chem."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"703","DOI":"10.1089\/ars.2008.2253","article-title":"3-Mercaptopyruvate sulfurtransferase produces hydrogen sulfide and bound sulfane sulfur in the brain","volume":"11","author":"Shibuya","year":"2009","journal-title":"Antioxid. Redox Signal."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1366","DOI":"10.1038\/ncomms2371","article-title":"A novel pathway for the production of hydrogen sulfide from d-cysteine in mammalian cells","volume":"4","author":"Shibuya","year":"2013","journal-title":"Nat. Commun."},{"key":"ref_24","first-page":"1511","article-title":"d-amino acid oxidase: Physiological role and applications","volume":"73","author":"Khoronenkova","year":"2008","journal-title":"Biochemistry"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"29","DOI":"10.1007\/978-3-319-18144-8_2","article-title":"Persulfidation (S-sulfhydration) and H2S","volume":"230","author":"Filipovic","year":"2015","journal-title":"Handb. Exp. Pharmacol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"457","DOI":"10.1038\/nchembio.1834","article-title":"Biogenesis of reactive sulfur species for signaling by hydrogen sulfide oxidation pathways","volume":"11","author":"Mishanina","year":"2015","journal-title":"Nat. Chem. Biol."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"3414","DOI":"10.1039\/C5SC04818D","article-title":"Improved tag-switch method reveals that thioredoxin acts as depersulfidase and controls the intracellular levels of protein persulfidation","volume":"7","author":"Wedmann","year":"2016","journal-title":"Chem. Sci."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"105","DOI":"10.1093\/jat\/13.2.105","article-title":"Determination of sulfide in brain tissue by gas dialysis\/ion chromatography: Postmortem studies and two case reports","volume":"13","author":"Goodwin","year":"1989","journal-title":"J. Anal. Toxicol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"848","DOI":"10.1139\/y03-077","article-title":"Modulation of endogenous production of H2S in rat tissues","volume":"81","author":"Zhao","year":"2003","journal-title":"Can. J. Physiol. Pharmacol."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"540","DOI":"10.1016\/S0378-4347(00)82537-2","article-title":"Determination of sulfide in brain tissue and rumen fluid by ion-interaction reversed-phase high-performance liquid chromatography","volume":"526","author":"Savage","year":"1990","journal-title":"J. Chromatogr. B Biomed. Sci. Appl."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1479","DOI":"10.1152\/ajpregu.90566.2008","article-title":"Whole tissue hydrogen sulfide concentrations are orders of magnitude lower than presently accepted values","volume":"295","author":"Furne","year":"2008","journal-title":"Am. J. Physiol. Regul. Integr. Comp. Physiol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"L403","DOI":"10.1152\/ajplung.00327.2014","article-title":"Working with nitric oxide and hydrogen sulfide in biological systems","volume":"308","author":"Yuan","year":"2015","journal-title":"Am. J. Physiol. Lung Cell. Mol. Physiol."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1346","DOI":"10.1016\/j.freeradbiomed.2009.09.018","article-title":"Making and working with hydrogen sulfide: The chemistry and generation of hydrogen sulfide in vitro and its measurement in vivo: A review","volume":"47","author":"Hughes","year":"2009","journal-title":"Free Radic. Biol. Med."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"1749","DOI":"10.1089\/ars.2012.5041","article-title":"Polysulfides link H2S to protein thiol oxidation","volume":"19","author":"Greiner","year":"2013","journal-title":"Antioxid. Redox Signal."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"876","DOI":"10.1016\/j.bbagen.2013.05.037","article-title":"Chemical aspects of hydrogen sulfide measurements in physiological samples","volume":"1840","author":"Nagy","year":"2014","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_36","first-page":"327","article-title":"Rhodanese","volume":"39","author":"Westley","year":"1973","journal-title":"Adv. Enzymol. Relat. Areas Mol. Biol."},{"key":"ref_37","first-page":"245","article-title":"Rhodanese and the sulfane pool","volume":"Volume 2","author":"Jacob","year":"1980","journal-title":"Enzymatic Basis of Detoxication"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"377","DOI":"10.1016\/S0272-0590(83)80008-6","article-title":"The sulfurtransferases","volume":"3","author":"Westley","year":"1983","journal-title":"Fundam. Appl. Toxicol."},{"key":"ref_39","first-page":"201","article-title":"Mammalian cyanide detoxification with sulphane sulphur","volume":"140","author":"Westley","year":"1988","journal-title":"CIBA Found. Symp."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1535","DOI":"10.1248\/bpb.17.1535","article-title":"Tissue and subcellular distribution of bound and acid-labile sulfur, and the enzymic capacity for sulfide production in the rat","volume":"17","author":"Ogasawara","year":"1994","journal-title":"Biol. Pharm. Bull."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"205","DOI":"10.1089\/ars.2008.2132","article-title":"A source of hydrogen sulfide and a mechanism of its release in the brain","volume":"11","author":"Ishigami","year":"2009","journal-title":"Antioxid. Redox Signal."},{"key":"ref_42","first-page":"1","article-title":"Cystathionine \u03b2-synthase, a key enzyme for homocysteine metabolism, is preferentially expressed in the radial glia\/astrocyte lineage of developing mouse CNS","volume":"24","author":"Enokido","year":"2005","journal-title":"FASEB J."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"243","DOI":"10.1007\/s004180050286","article-title":"Tissue and subcellular distribution of mercaptopyruvate sulfurtransferase in the rat: Confocal laser fluorescence and immunoelectron microscopic studies combined with biochemical analysis","volume":"110","author":"Nagahara","year":"1998","journal-title":"Histochem. Cell Biol."},{"key":"ref_44","doi-asserted-by":"crossref","unstructured":"Zhao, H., Chan, S.J., Ng, Y.K., and Wong, P.T.H. (2013). Brain 3-mercaptopyruvate sulfurtransferase (3MST): Cellular localization and downregulation after acute stroke. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0067322"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"33","DOI":"10.1016\/S0304-4165(96)00072-4","article-title":"Modification of liver cytosol enzyme activities promoted in vitro by reduced sulfur species generated from cystine with \u03b3-cystathionase","volume":"1334","author":"Ogasawara","year":"1997","journal-title":"Biochim. Biophys. Acta"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"3548","DOI":"10.1016\/j.febslet.2013.09.013","article-title":"Polysulfide exerts a protective effect against cytotoxicity caused by t-buthylhydroperoxide through Nrf2 signaling in neuroblastoma cells","volume":"587","author":"Koike","year":"2013","journal-title":"FEBS Lett."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"2451","DOI":"10.1096\/fj.12-226415","article-title":"Polysulfides are possible H2S-derived signaling molecules in rat brain","volume":"27","author":"Kimura","year":"2013","journal-title":"FASEB J."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"512","DOI":"10.1016\/j.freeradbiomed.2015.09.007","article-title":"Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is inactivated by S-sulfuration in vitro","volume":"89","author":"Jarosz","year":"2015","journal-title":"Free Radic. Biol. Med."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"26","DOI":"10.1002\/ana.10483","article-title":"Oxidative stress in Parkinson\u2019s disease","volume":"53","author":"Jenner","year":"2003","journal-title":"Ann. Neurol."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"134","DOI":"10.1016\/S0891-5849(96)00629-6","article-title":"Oxidative stress hypothesis in Alzheimer\u2019s disease","volume":"23","author":"Markesbery","year":"1997","journal-title":"Free Radic. Biol. Med."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"313","DOI":"10.1006\/bbrc.1997.6943","article-title":"An Nrf2 \/ small Maf heterodimer mediates the induction of phase II detoxifying enzyme genes through antioxidant response elements","volume":"322","author":"Itoh","year":"1997","journal-title":"Biochem. Biophys. Res. Commun."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"365","DOI":"10.1161\/CIRCRESAHA.109.199919","article-title":"Hydrogen sulfide mediates cardioprotection through Nrf2 signaling","volume":"105","author":"Calvert","year":"2009","journal-title":"Circ. Res."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"1215","DOI":"10.1152\/ajpheart.00796.2012","article-title":"Hydrogen sulfide preconditions the db\/db diabetic mouse heart against ischemia-reperfusion injury by activating Nrf2 signaling in an Erk-dependent manner","volume":"304","author":"Peake","year":"2013","journal-title":"Am. J. Physiol. Heart Circ. Physiol."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"465","DOI":"10.1089\/ars.2012.4944","article-title":"The gasotransmitter hydrogen sulfide induces Nrf2-target genes by inactivating the Keap1 ubiquitin ligase substrate adaptor through formation of a disulfide bond between Cys-226 and Cys-613","volume":"19","author":"Hourihan","year":"2013","journal-title":"Antioxid. Redox Signal."},{"key":"ref_55","doi-asserted-by":"crossref","first-page":"803","DOI":"10.1038\/nrm3391-c1","article-title":"The conversion of H2S to sulfane sulfur","volume":"13","author":"Toohey","year":"2012","journal-title":"Nat. Rev. Mol. Cell Biol."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"7606","DOI":"10.1073\/pnas.1321232111","article-title":"Reactive cysteine persulfides and S-polythiolation regulate oxidative stress and redox signaling","volume":"111","author":"Ida","year":"2014","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_57","doi-asserted-by":"crossref","first-page":"221","DOI":"10.1016\/j.bbrc.2015.01.140","article-title":"Dicarbonyl stress in cell and tissue dysfunction contributing to ageing and disease","volume":"458","author":"Rabbani","year":"2015","journal-title":"Biochem. Biophys. Res. Commun."},{"key":"ref_58","doi-asserted-by":"crossref","first-page":"1149","DOI":"10.1016\/S0002-9440(10)65659-3","article-title":"Advanced glycation end products in Alzheimer\u2019s disease and other neurodegenerative diseases","volume":"153","author":"Sasaki","year":"1998","journal-title":"Am. J. Pathol."},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"589","DOI":"10.1001\/archgenpsychiatry.2010.62","article-title":"Enhanced carbonyl stress in a subpopulation of schizophrenia carbonyl stress in schizophrenia","volume":"67","author":"Arai","year":"2010","journal-title":"Arch. Gen. Psychiatry"},{"key":"ref_60","doi-asserted-by":"crossref","first-page":"655","DOI":"10.1111\/pcn.12216","article-title":"Carbonyl stress and schizophrenia","volume":"68","author":"Arai","year":"2014","journal-title":"Psychiatry Clin. Neurosci."},{"key":"ref_61","doi-asserted-by":"crossref","first-page":"1093","DOI":"10.1089\/ars.2009.2918","article-title":"Interaction of methylglyoxal and hydrogen sulfide in rat vascular smooth muscle cells","volume":"12","author":"Chang","year":"2010","journal-title":"Antioxid. Redox Signal."},{"key":"ref_62","doi-asserted-by":"crossref","first-page":"102","DOI":"10.1016\/j.jchromb.2016.07.019","article-title":"Determination of methylglyoxal in human blood plasma using fluorescence high performance liquid chromatography after derivatization with 1,2-diamino-4,5-methylenedioxybenzene","volume":"1029\u20131030","author":"Ogasawara","year":"2016","journal-title":"J. Chromatogr. B Anal. Technol. Biomed. Life Sci."},{"key":"ref_63","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1016\/j.neuro.2016.05.003","article-title":"Polysulfides protect SH-SY5Y cells from methylglyoxal-induced toxicity by suppressing protein carbonylation: A possible physiological scavenger for carbonyl stress in the brain","volume":"55","author":"Koike","year":"2016","journal-title":"Neurotoxicology"},{"key":"ref_64","doi-asserted-by":"crossref","first-page":"3182","DOI":"10.1073\/pnas.1321871111","article-title":"Hydrogen sulfide cytoprotective signaling is endothelial nitric oxide synthase-nitric oxide dependent","volume":"111","author":"King","year":"2014","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"1405","DOI":"10.1053\/j.gastro.2005.02.034","article-title":"Cystathionine beta synthase deficiency promotes oxidative stress, fibrosis, and steatosis in mice liver","volume":"128","author":"Robert","year":"2005","journal-title":"Gastroenterology"}],"container-title":["Molecules"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1420-3049\/21\/12\/1753\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T19:29:01Z","timestamp":1760210941000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1420-3049\/21\/12\/1753"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2016,12,21]]},"references-count":65,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2016,12]]}},"alternative-id":["molecules21121753"],"URL":"https:\/\/doi.org\/10.3390\/molecules21121753","relation":{},"ISSN":["1420-3049"],"issn-type":[{"value":"1420-3049","type":"electronic"}],"subject":[],"published":{"date-parts":[[2016,12,21]]}}}