推 nanobio9:已請琇瑋唸一篇胡維碩老師的文章，與這個問題相關 08/06 16:22
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
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