Editing Israel Hanukoglu (section)

==Contributions to science==

Prof. Hanukoglu's scientific work concentrated in three different areas outlined below.

===Structures of keratins===
Hanukoglu's career in molecular biology started at the Department of Biochemistry of the [[University of Chicago]] (1980–1983 with [[Elaine Fuchs]]), where he cloned and sequenced cDNAs coding for cytoskeletal proteins, actin<ref name="pmid6842590">{{cite journal | vauthors = Hanukoglu I, Tanese N, Fuchs E | title = Complementary DNA sequence of a human cytoplasmic actin. Interspecies divergence of 3' non-coding regions | journal = Journal of Molecular Biology | volume = 163 | issue = 4 | pages = 673–8 | date = Feb 1983 | pmid = 6842590 | doi = 10.1016/0022-2836(83)90117-1 }}</ref> and alpha keratins.<ref name="1982-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Fuchs E | title = The cDNA sequence of a human epidermal keratin: divergence of sequence but conservation of structure among intermediate filament proteins. | journal = Cell | volume = 31 | issue = 1 | pages = 243–252 | date=Nov 1982 | doi = 10.1016/0092-8674(82)90424-X | pmid = 6186381 | s2cid = 35796315 |url=https://zenodo.org/record/890743}}</ref><ref name="1983-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Fuchs E | title = The cDNA sequence of a Type II cytoskeletal keratin reveals constant and variable structural domains among keratins. | journal = Cell | volume = 33 | issue = 3 | pages = 915–924 |date=Jul 1983 | doi = 10.1016/0092-8674(83)90034-X | pmid = 6191871 | s2cid = 21490380 |url=https://zenodo.org/record/890739}}</ref> He elucidated the first structures of cytoskeletal keratin families, and predicted the long helical domains of these proteins. By computerized analysis of amino acid sequences he predicted that the central rod domain of intermediate filament proteins is composed of four helical segments separated by three short linker sequences. Later crystallographic studies have confirmed this as a general model for intermediate filament protein structure.<ref name="pmid22705788">{{cite journal | vauthors = Lee CH, Kim MS, Chung BM, Leahy DJ, Coulombe PA | title = Structural basis for heteromeric assembly and perinuclear organization of keratin filaments | journal = Nature Structural & Molecular Biology | volume = 19 | issue = 7 | pages = 707–15 | date = Jul 2012 | pmid = 22705788 | doi = 10.1038/nsmb.2330 | pmc=3864793}}</ref><ref name="Hanukoglu-2014">{{Cite journal | vauthors = Hanukoglu I, Ezra L | title = Proteopedia: Coiled-coil structure of keratins. | journal = Biochem Mol Biol Educ | volume = 42 | issue = 1 | pages = 93–94 |date=Jan 2014 | doi = 10.1002/bmb.20746 | pmid = 24265184| s2cid = 30720797 | doi-access = free }}</ref>

===Steroid hormone synthesis===

During his Ph.D. thesis research, Israel isolated the mitochondrial enzymes that catalyze the first step in the synthesis of [[steroid hormones]] in all steroidogenic tissues, including the adrenal cortex, and the reproductive organs.<ref name="1981-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Spitsberg V, Bumpus JA, Dus KM, Jefcoate CR | title = Adrenal mitochondrial cytochrome P-450scc. Cholesterol and adrenodoxin interactions at equilibrium and during turnover | journal = The Journal of Biological Chemistry | volume = 256 | issue = 9 | pages = 4321–8 | date = May 1981 | doi = 10.1016/S0021-9258(19)69436-6 | pmid = 7217084 | doi-access = free }}</ref> The first step of steroidogenesis is dependent on the transfer of electrons from NADPH to a P450 type enzyme ([[P450scc]]) via an electron-transfer chain that includes two additional proteins.<ref name="1992-Hanukoglu">{{cite journal | vauthors = Hanukoglu I | title = Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 43 | issue = 8 | pages = 779–804 | date = Dec 1992 | pmid = 22217824 | doi = 10.1016/0960-0760(92)90307-5 | s2cid = 112729 |url=https://zenodo.org/record/890723}}</ref> These proteins are located on the inner mitochondrial membrane.<ref name="1990-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Suh BS, Himmelhoch S, Amsterdam A | title = Induction and mitochondrial localization of cytochrome P450scc system enzymes in normal and transformed ovarian granulosa cells | journal = The Journal of Cell Biology | volume = 111 | issue = 4 | pages = 1373–81 | date = October 1990 | pmid = 2170421 | pmc = 2116250 | doi = 10.1083/jcb.111.4.1373 }}</ref> Israel reconstituted this system using proteins he purified,  characterized the process of electron transfer between the proteins, and built a kinetic model that simulated precisely the dynamic behavior of this complex system.<ref name="1980-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Jefcoate CR | title = Mitochondrial cytochrome P-450scc. Mechanism of electron transport by adrenodoxin | journal = The Journal of Biological Chemistry | volume = 255 | issue = 7 | pages = 3057–61 | date = Apr 1980 | doi = 10.1016/S0021-9258(19)85851-9 | pmid = 6766943 | url = http://www.jbc.org/content/255/7/3057.full.pdf | doi-access = free }}</ref><ref name="1981-Hanukoglu" />

In his first academic position at the Department of Biology at the [[Technion-Israel Institute of Technology]], he first determined the molar stoichiometry of the mitochondrial P450 system proteins using specific antibodies that he generated.<ref name="1987-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Hanukoglu Z | title = Stoichiometry of mitochondrial cytochromes P-450, adrenodoxin and adrenodoxin reductase in adrenal cortex and corpus luteum. Implications for membrane organization and gene regulation | journal = European Journal of Biochemistry | volume = 157 | issue = 1 | pages = 27–31 | date = May 1986 | pmid = 3011431 | doi = 10.1111/j.1432-1033.1986.tb09633.x | url = https://zenodo.org/record/890737 | doi-access = free }}</ref> He then set out to clone the cDNAs and the genes that code for these enzymes. His lab was the first to clone the cDNAs and the gene coding for [[adrenodoxin reductase]] - the first enzyme in the electron transfer chain of the mitochondrial P450 system.<ref name="1986-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Gutfinger T, Haniu M, Shively JE | title = Isolation of a cDNA for adrenodoxin reductase (ferredoxin-NADP+ reductase). Implications for mitochondrial cytochrome P-450 systems. | journal = European Journal of Biochemistry | volume = 169 | issue = 3 | pages = 449–455 |date=Dec 1987 | doi = 10.1111/j.1432-1033.1987.tb13632.x | pmid = 3691502 | url=https://zenodo.org/record/890735 | doi-access = free }}</ref><ref name="1989-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Gutfinger T | title = cDNA sequence of adrenodoxin reductase. Identification of NADP-binding sites in oxidoreductases | journal = European Journal of Biochemistry | volume = 180 | issue = 2 | pages = 479–84 | date = Mar 1989 | pmid = 2924777 | doi = 10.1111/j.1432-1033.1989.tb14671.x|url=https://zenodo.org/record/890733 | doi-access = free }}</ref><ref name="1988-Solish">{{cite journal | vauthors = Solish SB, Picado-Leonard J, Morel Y, Kuhn RW, Mohandas TK, Hanukoglu I, Miller WL | title = Human adrenodoxin reductase: two mRNAs encoded by a single gene on chromosome 17cen----q25 are expressed in steroidogenic tissues | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 85 | issue = 19 | pages = 7104–7108 | date = Oct 1988 | pmid = 2845396 | pmc = 282132 | doi = 10.1073/pnas.85.19.7104 | bibcode = 1988PNAS...85.7104S | doi-access = free }}</ref>

By sequence and structural analyses of adrenodoxin reductase, Israel identified its binding sites for the electron donor and acceptor coenzymes, NADPH and FAD.<ref name="1989-Hanukoglu" /> By sequence analyses of the large oxidoreductase type of enzyme families, he noted that the FAD-binding site is a classical [[Rossmann fold]], but the NADPH binding site has a different consensus sequence that could be responsible for NAD vs. NADP coenzyme specificity. The importance of the motifs he identified was confirmed by re-engineering of coenzyme specificities of different enzymes.<ref name="pmid2296288">{{cite journal | vauthors = Scrutton NS, Berry A, Perham RN | title = Redesign of the coenzyme specificity of a dehydrogenase by protein engineering | journal = Nature | volume = 343 | issue = 6253 | pages = 38–43 | date = Jan 1990 | pmid = 2296288 | doi = 10.1038/343038a0 | bibcode = 1990Natur.343...38S | s2cid = 1580419 }}</ref> Elucidation of the crystal structure of adrenodoxin reductase further verified Israel's identification of the coenzyme binding sites.<ref name="1999-Ziegler">{{cite journal | vauthors = Ziegler GA, Vonrhein C, Hanukoglu I, Schulz GE | title = The structure of adrenodoxin reductase of mitochondrial P450 systems: electron transfer for steroid biosynthesis | journal = Journal of Molecular Biology | volume = 289 | issue = 4 | pages = 981–90 | date = Jun 1999 | pmid = 10369776 | doi = 10.1006/jmbi.1999.2807 }}</ref> Analysis of the phylogeny of this enzyme in eukaryotes showed that the NADP binding site sequence is strictly conserved.<ref name="2017-Hanukoglu-JME">{{cite journal | vauthors = Hanukoglu I | title = Conservation of the Enzyme-Coenzyme Interfaces in FAD and NADP Binding Adrenodoxin Reductase-A Ubiquitous Enzyme | journal = Journal of Molecular Evolution | volume = 85 | issue= 5 | pages= 205–218 | year= 2017 | pmid= 29177972 | doi= 10.1007/s00239-017-9821-9 | bibcode = 2017JMolE..85..205H | s2cid = 7120148 }}</ref>

As the steroidogenic tissues have very high levels of antioxidants, Israel suspected that the P450 systems may leak electrons producing oxygen radicals. He examined this issue and showed that indeed, electrons that leak during the action mitochondrial P450 systems generate reactive oxygen species.<ref name="1993-Hanukoglu">{{cite journal | vauthors = Hanukoglu I, Rapoport R, Weiner L, Sklan D | title = Electron leakage from the mitochondrial NADPH-adrenodoxin reductase-adrenodoxin-P450scc (cholesterol side chain cleavage) system | journal = Archives of Biochemistry and Biophysics | volume = 305 | issue = 2 | pages = 489–98 | date = September 1993 | pmid = 8396893 | doi = 10.1006/abbi.1993.1452 | url = https://zenodo.org/record/890721 }}</ref><ref name="1995-Rapoport">{{cite journal | vauthors = Rapoport R, Sklan D, Hanukoglu I | title=Electron leakage from the adrenal cortex mitochondrial P450scc and P450c11 systems: NADPH and steroid dependence.|journal=Archives of Biochemistry and Biophysics|date=10 March 1995|volume=317|issue=2|pages=412–6|pmid=7893157 | doi= 10.1006/abbi.1995.1182| url=https://zenodo.org/record/890751}}</ref><ref name="2006-Hanukoglu">{{cite journal | vauthors = Hanukoglu I | title = Antioxidant protective mechanisms against reactive oxygen species (ROS) generated by mitochondrial P450 systems in steroidogenic cells | journal = Drug Metabolism Reviews | volume = 38 | issue = 1–2 | pages = 171–96 | year = 2006 | pmid = 16684656 | doi = 10.1080/03602530600570040| s2cid = 10766948 |url=https://zenodo.org/record/890701 }}</ref> His studies also showed that in bovine ovary, levels of antioxidants are coordinately regulated with steroidogenesis.<ref name="1998-Rapoport">{{cite journal | vauthors = Rapoport R, Sklan D, Wolfenson D, Shaham-Albalancy A, Hanukoglu I | title = Antioxidant capacity is correlated with steroidogenic status of the corpus luteum during the bovine estrous cycle | journal = Biochim. Biophys. Acta | volume = 1380 | issue = 1 | pages = 133–40 |date=March 1998 | pmid = 9545562 | doi = 10.1016/S0304-4165(97)00136-0|url=https://zenodo.org/record/890705 }}</ref>

His other work in this field includes elucidation of the mechanism of action of corticotropin ([[ACTH]]) in regulating steroid hormone synthesis in the adrenal cortex,<ref name="1990-Hanukoglu-b">{{cite journal | vauthors = Hanukoglu I, Feuchtwanger R, Hanukoglu A | title = Mechanism of corticotropin and cAMP induction of mitochondrial cytochrome P450 system enzymes in adrenal cortex cells | journal = The Journal of Biological Chemistry | volume = 265 | issue = 33 | pages = 20602–8 | date = Nov 1990 | doi = 10.1016/S0021-9258(17)30545-8 | pmid = 2173715 | url = https://zenodo.org/record/890729 | doi-access = free }}</ref><ref name="1993-Raikhinstein">{{cite journal | vauthors = Raikhinstein M, Hanukoglu I | title = Mitochondrial-genome-encoded RNAs: differential regulation by corticotropin in bovine adrenocortical cells | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 90 | issue = 22 | pages = 10509–13 | date = Nov 1993 | pmid = 7504267 | pmc = 47806 | doi = 10.1073/pnas.90.22.10509 | bibcode = 1993PNAS...9010509R | doi-access = free }}</ref> regulation of adrenal steroidogenic capacity in disease states,<ref name="1995-Hanukoglu-A">{{cite journal | vauthors = Hanukoglu A, Fried D, Nakash I, Hanukoglu I | title = Selective increases in adrenal steroidogenic capacity during acute respiratory disease in infants. | journal = Eur J Endocrinol | volume = 133 | issue = 5 | pages = 552–6 |date=Nov 1995 | doi = 10.1530/eje.0.1330552 | pmid = 7581984 | s2cid = 44439040 }}</ref> and the cloning and elucidation of the structure of ACTH receptor.<ref name="1994-Raikhinstein">{{cite journal | vauthors = Raikhinstein M, Zohar M, Hanukoglu I | title = cDNA cloning and sequence analysis of the bovine adrenocorticotropic hormone (ACTH) receptor | journal = Biochimica et Biophysica Acta (BBA) - Molecular Cell Research | volume = 1220 | issue = 3 | pages = 329–32 | date = Feb 1994 | pmid = 8305507 | doi = 10.1016/0167-4889(94)90157-0 |url=https://zenodo.org/record/890717}}</ref>

In this field, Israel organized the first International Symposium in Molecular Steroidogenesis in [[Jerusalem]] in 1991 which served as the cornerstone for a continuing series of  international symposia for scientists who specialize in this field.<ref name="pmid22217821">{{Cite journal  | last1 = Hanukoglu | first1 = I. | title = Current research on steroid metabolism: transition from biochemistry to molecular-cell biology. | journal = J Steroid Biochem Mol Biol | volume = 43 | issue = 8 | pages = 745–9 |date=Dec 1992 | doi = 10.1016/0960-0760(92)90304-2 | pmid = 22217821 | s2cid = 5789778 }}</ref>

===Epithelial sodium channel (ENaC)===

In his clinical work as an endocrinologist, Israel's older brother, Prof. [[Aaron Hanukoglu]] ([[Tel Aviv University]], Sackler Medical School and E. Wolfson Medical Center), identified that a hereditary disease named pseudohypoaldosteronism (PHA) type I encompasses two independent syndromes.<ref name="1991-Hanukoglu" >{{cite journal | vauthors = Hanukoglu A | title = Type I pseudohypoaldosteronism includes two clinically and genetically distinct entities with either renal or multiple target organ defects | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 73 | issue = 5 | pages = 936–44 | date = November 1991 | pmid = 1939532 | doi = 10.1210/jcem-73-5-936 | url = https://zenodo.org/record/890914 }}</ref> Following this discovery the two brothers continued their collaboration to understand the molecular basis of the severe form of PHA.

By their collaborative work that also included additional labs, the Hanukoglu brothers discovered that the severe forms of pseudohypoaldosteronism type I result from mutations in three genes ([[SCNN1A]], [[SCNN1B]], and [[SCNN1B]]) that encode for protein subunits of the Epithelial sodium (Na<sup>+</sup>) channel (ENaC).<ref name="pmid8824886">{{cite journal | vauthors = Strautnieks SS, Thompson RJ, Hanukoglu A, Dillon MJ, Hanukoglu I, Kuhnle U, Seckl J, Gardiner RM, Chung E | title = Localisation of pseudohypoaldosteronism genes to chromosome 16p12.2-13.11 and 12p13.1-pter by homozygosity mapping | journal = Human Molecular Genetics | volume = 5 | issue = 2 | pages = 293–9 | date = February 1996 | pmid = 8824886 | doi = 10.1093/hmg/5.2.293 | doi-access = free }}</ref><ref name="pmid8589714">{{cite journal | vauthors = Chang SS, Grunder S, Hanukoglu A, Rösler A, Mathew PM, Hanukoglu I, Schild L, Lu Y, Shimkets RA, Nelson-Williams C, Rossier BC, Lifton RP | title = Mutations in subunits of the epithelial sodium channel cause salt wasting with hyperkalaemic acidosis, pseudohypoaldosteronism type 1 | journal = Nature Genetics | volume = 12 | issue = 3 | pages = 248–53 | date = March 1996 | pmid = 8589714 | doi = 10.1038/ng0396-248 | s2cid = 8185511 }}</ref><ref name="pmid12107247">{{cite journal | vauthors = Saxena A, Hanukoglu I, Saxena D, Thompson RJ, Gardiner RM, Hanukoglu A | title = Novel mutations responsible for autosomal recessive multisystem pseudohypoaldosteronism and sequence variants in epithelial sodium channel alpha-, beta-, and gamma-subunit genes | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 87 | issue = 7 | pages = 3344–50 | date = July 2002 | pmid = 12107247 | doi = 10.1210/jcem.87.7.8674 | doi-access = free }}</ref><ref name="pmid15853823">{{cite journal | vauthors = Edelheit O, Hanukoglu I, Gizewska M, Kandemir N, Tenenbaum-Rakover Y, Yurdakök M, Zajaczek S, Hanukoglu A | title = Novel mutations in epithelial sodium channel (ENaC) subunit genes and phenotypic expression of multisystem pseudohypoaldosteronism | journal = Clinical Endocrinology | volume = 62 | issue = 5 | pages = 547–53 | date = May 2005 | pmid = 15853823 | doi = 10.1111/j.1365-2265.2005.02255.x | s2cid = 2749562 }}</ref> These studies also helped establish that ENaC is the principal channel involved in blood volume and blood pressure regulation in humans.<ref name="2016-Hanukoglu" >{{cite journal | vauthors = Hanukoglu I, Hanukoglu A | title = Epithelial sodium channel (ENaC) family: Phylogeny, structure-function, tissue distribution, and associated inherited diseases | journal = Gene | volume = 579 | issue = 2 | pages = 95–132 | date = April 2016 | pmid = 26772908 | pmc = 4756657 | doi = 10.1016/j.gene.2015.12.061 }}</ref>

Following these studies, the Hanukoglu brothers directed their attention to understand the structure and function of ENaC assembled from normal and mutated subunits. Their analyses showed that the phenotypic variations in the severity of pseudohypoaldosteronism are associated with the types of genetic mutations.<ref>{{cite journal | vauthors = Hanukoglu A, Edelheit O, Shriki Y, Gizewska M, Dascal N, Hanukoglu I | title = Renin-aldosterone response, urinary Na/K ratio and growth in pseudohypoaldosteronism patients with mutations in epithelial sodium channel (ENaC) subunit genes | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 111 | issue = 3–5 | pages = 268–74 | date = September 2008 | pmid = 18634878 | doi = 10.1016/j.jsbmb.2008.06.013 | s2cid = 24688546 }}</ref><ref>{{cite journal | vauthors = Edelheit O, Hanukoglu I, Shriki Y, Tfilin M, Dascal N, Gillis D, Hanukoglu A | title = Truncated beta epithelial sodium channel (ENaC) subunits responsible for multi-system pseudohypoaldosteronism support partial activity of ENaC | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 119 | issue = 1–2 | pages = 84–8 | date = March 2010 | pmid = 20064610 | doi = 10.1016/j.jsbmb.2010.01.002 | s2cid = 9564777 }}</ref> Their work on the structure of ENaC subunits led to the identification of charged residues and regions responsible for transport of the protein to membrane and for regulation of extracellular Na<sup>+</sup> ions.<ref name="2011-Edelheit">{{cite journal | vauthors = Edelheit O, Hanukoglu I, Dascal N, Hanukoglu A | title = Identification of the roles of conserved charged residues in the extracellular domain of an epithelial sodium channel (ENaC) subunit by alanine mutagenesis | journal = American Journal of Physiology. Renal Physiology | volume = 300 | issue = 4 | pages = F887-97 | date = April 2011 | pmid = 21209000 | doi = 10.1152/ajprenal.00648.2010 | s2cid = 869654 }}</ref><ref name="2014-Edelheit">{{cite journal | vauthors = Edelheit O, Ben-Shahar R, Dascal N, Hanukoglu A, Hanukoglu I | title = Conserved charged residues at the surface and interface of epithelial sodium channel subunits--roles in cell surface expression and the sodium self-inhibition response | journal = The FEBS Journal | volume = 281 | issue = 8 | pages = 2097–111 | date = April 2014 | pmid = 24571549 | doi = 10.1111/febs.12765 | s2cid = 5807500 | doi-access = free }}</ref>

In an extensive review of studies on ASIC and ENaC, Prof. Hanukoglu has summarized the major similarities between [[ASIC]] and ENaC type channels.<ref>{{cite journal | vauthors = Hanukoglu I | title = ASIC and ENaC type sodium channels: Conformational states and the structures of the ion selectivity filters | journal = The FEBS Journal | volume =  284| issue =  4| pages = 525–545 | date = August 2016 | pmid = 27580245 | doi = 10.1111/febs.13840 | s2cid = 24402104 | url = https://zenodo.org/record/890906 }}</ref>

To define the sites of localization of ENaC in tissues and within cells, Hanukoglu's laboratory generated polyclonal antibodies against extracellular ENaC subunits. These antibodies for the first time permitted visualization of intracellular localization of ENaC at high resolution and led to the discovery that in all cells with motile cilia ENaC is located on cilia.<ref name="pmid22207244">{{cite journal | vauthors = Enuka Y, Hanukoglu I, Edelheit O, Vaknine H, Hanukoglu A | title = Epithelial sodium channels (ENaC) are uniformly distributed on motile cilia in the oviduct and the respiratory airways | journal = Histochemistry and Cell Biology | volume = 137 | issue = 3 | pages = 339–53 | date = March 2012 | pmid = 22207244 | doi = 10.1007/s00418-011-0904-1 | s2cid = 15178940 }}</ref> These studies establish that ENaC is an important regulator of fluid level in the luminal side of cells with motile cilia in the female reproductive and respiratory tract.<ref name="pmid22207244" /> More recently, they showed that these sodium channels are also located in the seminiferous tubules in the testis and in the tail and head region of sperm.<ref name="Sharma-2018">{{cite journal|vauthors=Sharma S, Hanukoglu A, Hanukoglu I | title=Localization of epithelial sodium channel (ENaC) and CFTR in the germinal epithelium of the testis, Sertoli cells, and spermatozoa. | journal=Journal of Molecular Histology | year= 2018 | volume= 49 | issue= 2 | pages= 195–208 | pmid=29453757 | doi=10.1007/s10735-018-9759-2 | s2cid=3761720 }}</ref>

Systemic pseudohypoaldosteronism patients with mutated ENaC subunits may lose significant amount salt in sweat especially at hot climates.<ref name="1991-Hanukoglu" /> To identify the sites of salt loss, Hanukoglu brothers examined the localization of ENaC in the human skin.<ref name="2017-Hanukoglu-2">{{cite journal | vauthors = Hanukoglu I, Boggula VR, Vaknine H, Sharma S, Kleyman T, Hanukoglu A | title = Expression of epithelial sodium channel (ENaC) and CFTR in the human epidermis and epidermal appendages | journal = Histochemistry and Cell Biology | volume = 147 | issue = 6 | pages = 733–748 | date = January 2017 | pmid = 28130590 | doi = 10.1007/s00418-016-1535-3 | s2cid = 8504408 |url=https://zenodo.org/record/890756}}</ref> In a comprehensive study examining all the layers of skin and epidermal appendages, they found a widespread distribution of ENaC in keratinocytes in the epidermal layers. Yet, in the eccrine sweat glands, ENaC was localized on the apical cell membrane exposed to the duct of these sweat glands. Based on additional observations, they concluded that the ENaC located on the eccrine gland sweat ducts is responsible for the uptake of Na<sup>+</sup> ions from sweat secretions. This recycling of Na<sup>+</sup> reduces the concentration of salt in perspiration and prevents the loss of salt at hot climates via [[perspiration]].<ref name="2017-Hanukoglu-2" />