終於找到了Orz http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mcb.section.4816 The different structures of N- and O-linked oligosaccharides reflect differences in their biosynthesis. O-linked sugars are added one at a time, and each sugar transfer is catalyzed by a different glycosyltransferase enzyme. In contrast, biosynthesis of N-linked oligosaccharides begins with the addition of a large preformed oligosaccharide, containing 14 sugar residues; subsequently certain sugar residues are removed and others are added, one at a time, in a defined order with each reaction catalyzed by a different enzyme. As described below, the various steps in the formation of both O- and N-linked oligosaccharides occur in specific organelles. O-linked Enzyme是一個一個把糖接上去的 N-linked Enzyme是接完一串之後再修飾小部分 每個過程都有不同的酵素參與(換句話說就是酵素的構型決定Sequence) All known glycosyltransferases that act on secretory proteins are integral membrane proteins with active sites facing the lumen of the organelle. Each glycosyltransferase is specific for both the donor sugar nucleotide and the acceptor molecule. The galactosyltransferase depicted in Figure 17-32, for instance, only transfers a galactose residue (from UDP-galactose), and only to the 3 carbon atom of an acceptor N-acetylgalactosamine residue. A different enzyme transfers galactose to the 4 carbon of N-acetylglucosamine, and yet another transfers galactose to the 3 carbon of galactose. 目前已知作用在外泌蛋白的醣轉移酵素都是胞器膜上的鑲膜蛋白 每個醣轉移酵素只針對特定的糖和受體有作用 舉個例子 某些galactosyltransferase只轉移UDP-gal.的gal.到N-acetylgalactosamine的3號碳上 而其他種類的galactosyltransferase卻可以轉到N-acetylglucosamine的4號碳等等 --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 140.112.199.125