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T. Akama, M.N. Fukuda; Responsible Enzymes for Corneal Keratan Sulfate . Invest. Ophthalmol. Vis. Sci. 2003;44(13):851.
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Purpose: Keratan sulfate proteoglycans are found in human cornea and thought to be involved in maintaining of corneal transparency. To understand biosynthetic pathway of corneal keratan sulfate carbohydrate chain, we analyzed the presence of mRNAs of candidate enzymes for keratan sulfate production. Methods: ß-1,3-N-acetylglucosaminyltransferases (GnTs) and ß-1,4-galactosyltransferases (GalTs) are involved in extension of keratan sulfate carbohydrate chain. We prepared specific primer pairs for mRNAs of seven GnTs and seven GalTs. We also prepared corneal cDNA library from human corneas obtained from San Diego Eye Bank and analyzed the presence of mRNA of GnTs and GalTs in the corneal cDNA by RT-PCR. Results: By RT-PCR analysis, 6 out of 7 GnT mRNAs (GnT1 to GnT7, except GnT6, and iGnT) and all the GalT mRNAs (GalT1to GalT7) analyzed were detected in human cornea cDNA library. Since GnT2 and GalT1 are the most active glycosyltransferases for each GlcNAc and Gal, we also analyzed GnT2 and GalT1 activity for keratan sulfate production in vitro and confirmed that the glycosyltransferases produce keratan sulfate disaccharide repeat in cooperation with carbohydrate sulfotransferases in vitro. Conclusions: More than one mRNA for each GnT and GalT was detected in human cornea, suggesting that multiple GnT and GalT enzymes are involved in processing of corneal keratan sulfate carbohydrate. Since keratan sulfate carbohydrate is one of the most abundant carbohydrates in the cornea, a large quantity of the carbohydrate produced by multiple enzymes may be necessary for maintenance of corneal transparency.
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