O-linked

Fig. 3. Human CG, hLH, and equine CG (eCG) P-subunits. Amino acid numbeiing is relative to maximum homology between the three subunits. Consensus glycosylation sites ate at Asn-13 and 30. = same amino acid as hCG/3. Underlined Asn residues indicate attachment of N-linked carbohydrate chains. Serines at positions 121, 127, 132, and 138 of hCGP are underlined to indicate sites of O-linked carbohydrate attachment. Residues 115—118,...

N-Linked substituents O-Linked substituents S-Linked substituents C-Linked substituents Reactivity at the Ring Nitrogen Atoms Reduction Oxidation... 

The siloxane Si—O link has a number of interesting properties which are relevant to the properties of the polyorganosiloxanes. TTiese will be dealt with later. 

FIGURE 9.26 The carbohydrate tnoiedes of glycoproteins may be linked to the protein via (a) serine or threonine residues (in the O-linked saccharides) or (b) asparagine residues (in the N-linked saccharides), (c) N-Linked glycoproteins are of three types high mannose, complex, and hybrid, the latter of which combines structures found in the high mannose and complex saccharides. 

A unique family of O-linked glycoproteins permits fish to live in the icy seawater of the Arctic and Antarctic regions where water temperature may reach as low as — 1.9°C. Antifreeze glycoproteins (AFGPs) are found in the blood of nearly all Antarctic fish and at least five Arctic fish. These glycoproteins have the peptide structure... 

FIGURE 9.31 The known proteoglycans include a variety of structures. The carbohydrate groups of proteoglycans are predominantly glycosaminoglycans O-linked to serine residues. Proteoglycans include both soluble proteins and integral transmembrane proteins. 

Suggest a structural or functional role for the O-linked saccharide domain in the LDL receptor (Figure 25.40). 

In a typical reaction, a series of C - O linked pyrazinone-triazoles were irradiated with an excess (3.5 equiv) of DMAD in o-DCB. The reactions were completed in 6-20 min at 180 °C, using a maximum irradiation power of 200 W. After spontaneous elimination of the corresponding isocyanate or cyanogen chloride, the pyridines and pyridinones were formed in combined yields of 71-99%. It is noteworthy that the pyrazinones with an aryl moiety at the N-1 position yielded pyridines as major products, while those with ben-zyUc or alkyl ester moieties at the N-1 position furnished the corresponding pyridinones as major products. 

Scheme 28 Diels-Alder reactions of C - O linked 2( l//)-pyrazinone-triazoles with DMAD...

Mucins Have a High Content of O-Linked Oligosaccharides Exhibit Repeating Amino Acid Sequences... 

The Biosynthesis of O-Linked Glycoproteins Uses Nucleotide Sugars... 

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