Glycosylated amino acids, periodate

The degree of glycosylation of the glycopolypeptides was estimated via H NMR, MALDI-TOF, and periodate assay (Glycoprotein Carbohydrate Estimation Kit (Pierce, Rockford, IL). H NMR spectra were acquired on a Bruker DRX-400 NMR spectrometer under standard quantitative conditions at 25 °C, and the standard protocols for the periodate assay were as described by the manufacturer. Comparison of sample solutions to a calibration curve of proteins of known carbohydrate content, combined with quantitative amino acid analysis of the samples, permitted estimation of the degree of substitution of the glycopolypeptides. 

The chemistry of the browning reaction has been reviewed periodically (1-7). The carbohydrate-amino acid browning reaction produces literally hundreds of reaction products. Despite the fact that the Maillard reaction has been investigated for many years, we cannot as yet identify all the reactant compounds. The first steps are, however, clearly established. The aldose or ketose reacts with amine to produce N-substituted glycosyl amine (Fig. 1). This rearranges, as illustrated, to produce a 1-amino-desoxy-2-ketosyl amine. If it is blocked, the overall reaction is blocked. This key compound or compounds can then continue to react (Fig. 2). The desoxy-ketose or amadori rearrangement product can dehydrate to produce furfural-like compounds or, through the loss of water, produce reductones. All of these compounds can react with one another or with other amine compounds to produce a wide variety of reaction products. 

The cell walls of Streptococcus pneumoniae contain a teichoic acid (C polysaccharide) composed of 2-acetamido-2-deoxy-D-galactose, 2-acetamido-4-amino-2,4,6-trideoxy-D-hexose, ribitol phosphate, choline phosphate, and D-glucose. From the results of periodate oxidation and methylation analysis, together with an examination of the n.m.r. spectra, the structure (1) has been proposed. It is speculated that the C-3 hydroxy-group of the chain terminal diaminotrideoxy-D-hexose unit is glycosylated with isomaltose. 

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