Transcobalamin I (TC-1), also known as haptocorrin (HC), R-factor, and R-protein is encoded in the human by the TCN1 gene. TC-1 is a glycoprotein produced by the salivary glands of the mouth. It primarily serves to protect cobalamin (Vitamin B12) from acid degradation in the stomach by producing a HC-Vitamin B12 complex. Once the complex has traveled to the more pH-neutral duodenum, pancreatic proteases degrade haptocorrin, releasing free cobalamin, which now binds to intrinsic factor for absorption by ileal enterocytes.
Separate from the digestive absorption function, serum TC-1 binds 80-90% of circulating B12, rendering it unavailable for cellular delivery by TC-2.[1] Several serious, even life-threatening diseases cause elevated serum HC, measured as abnormally high serum vitamin B12.[2]
Transcobalamin II (TC-2), a nonglycoprotein secretory protein of molecular mass 43 kDa, is encoded in the human by the TCN2 gene. TC-2 binds cobalamin once it has been taken up by enterocytes of the terminal ileum and the "Intrinsic Factor-Vitamin B12" complex has been degraded. TC-2 is then involved with the transport of Vitamin B12 to the tissues, where it binds to its plasma membrane receptor (TC-2R), a heavily glycosylated protein with a monomeric molecular mass of 62 kDa, and releases cobalamin to the cells.[3]
Referencesedit
^McCorvie TJ, Ferreira D, Yue WW, Froese DS (May 2023). "The complex machinery of human cobalamin metabolism". J Inherit Metab Dis. 46 (3): 406–20. doi:10.1002/jimd.12593. PMID 36680553.
^Seetharam B, Li N (2000). "Transcobalamin II and its cell surface receptor". Vitam Horm. 59: 337–66. doi:10.1016/s0083-6729(00)59012-8. PMID 10714245.
transcobalamin, carrier, proteins, which, bind, cobalamin, transcobalamin, vitamin, binding, protein, binder, family, identifierssymboltcn1ncbi, gene6947hgnc11652omim189905refseqnm, 001062uniprotp20061other, datalocuschr, q12search, forstructuresswiss, modeldo. Transcobalamins are carrier proteins which bind cobalamin B12 transcobalamin I vitamin B12 binding protein R binder family IdentifiersSymbolTCN1NCBI gene6947HGNC11652OMIM189905RefSeqNM 001062UniProtP20061Other dataLocusChr 11 q11 q12Search forStructuresSwiss modelDomainsInterPro transcobalamin II macrocytic anemiaIdentifiersSymbolTCN2NCBI gene6948HGNC11653OMIM275350PDB2BB5RefSeqNM 000355UniProtP20062Other dataLocusChr 22 q11 2 qterSearch forStructuresSwiss modelDomainsInterProTypes editTranscobalamin I TC 1 also known as haptocorrin HC R factor and R protein is encoded in the human by the TCN1 gene TC 1 is a glycoprotein produced by the salivary glands of the mouth It primarily serves to protect cobalamin Vitamin B12 from acid degradation in the stomach by producing a HC Vitamin B12 complex Once the complex has traveled to the more pH neutral duodenum pancreatic proteases degrade haptocorrin releasing free cobalamin which now binds to intrinsic factor for absorption by ileal enterocytes Separate from the digestive absorption function serum TC 1 binds 80 90 of circulating B12 rendering it unavailable for cellular delivery by TC 2 1 Several serious even life threatening diseases cause elevated serum HC measured as abnormally high serum vitamin B12 2 Transcobalamin II TC 2 a nonglycoprotein secretory protein of molecular mass 43 kDa is encoded in the human by the TCN2 gene TC 2 binds cobalamin once it has been taken up by enterocytes of the terminal ileum and the Intrinsic Factor Vitamin B12 complex has been degraded TC 2 is then involved with the transport of Vitamin B12 to the tissues where it binds to its plasma membrane receptor TC 2R a heavily glycosylated protein with a monomeric molecular mass of 62 kDa and releases cobalamin to the cells 3 References edit McCorvie TJ Ferreira D Yue WW Froese DS May 2023 The complex machinery of human cobalamin metabolism J Inherit Metab Dis 46 3 406 20 doi 10 1002 jimd 12593 PMID 36680553 Ermens AA Vlasveld LT Lindemans J November 2003 Significance of elevated cobalamin vitamin B12 levels in blood Clin Biochem 36 8 585 90 doi 10 1016 j clinbiochem 2003 08 004 PMID 14636871 Seetharam B Li N 2000 Transcobalamin II and its cell surface receptor Vitam Horm 59 337 66 doi 10 1016 s0083 6729 00 59012 8 PMID 10714245 External links editTranscobalamins at the U S National Library of Medicine Medical Subject Headings MeSH Retrieved from https en wikipedia org w index php title Transcobalamin amp oldid 1222303909, wikipedia, wiki, book, books, library,
