Glycopeptide amino acid composition

To obtain data on the heterogeneity of the glycopeptide fraction of microbubble surfactant, comparative amino acid analyses were performed on two of the major peaks obtained from gel filtration. From the ratio of absorbances at 230 and 280 nm (ref. 265) and the elution profile shown in Fig. 5.3, it appeared that peaks I and III would differ the most in amino acid composition and, therefore, these two peaks were selected for amino acid analysis. Peak I was sufficiently large to be divided into three equal aliquots and peak III into two equal aliquots for automated analysis. Peak II, which eluted closest (Fig. 5.3) to the dominant peak I and presumably was most similar in molecular composition to this large initial peak, was analyzed separately by HPLC for carbohydrate content. 

Table 5.2 lists the amino acid molar ratios determined for LHCP from several plant sources, and compares these results with the mean values obtained for the main glycopeptide subfraction (peak I in Table 5.1) from microbubble surfactant. It can be seen from Table 5.2 that the amino acid composition of LHCP clearly resembles that of the main glycopeptide subfraction. Specifically, in both cases nonpolar residues represent a majority and near constant fraction (i.e., 59-62%) of the amino acid composition, with the relative amounts of such residues in practically all individual cases listed following the pattern glycine > leucine, alanine, valine, proline > isoleucine, phenylalanine > methionine, tryptophan (Table 5.2). Accordingly, the glycopeptide fraction of microbubble surfactant may represent a degradation product of the light-harvesting chlorophyll a/b-protein, which is well known (ref. 373-375) to be extremely widely distributed in terrestrial, freshwater, and salt-water environments (cf. ref. 379).

Compound 13 is one of the tetra-antennary, asialo glycopeptides, isolated from asialo a,-acid glycoprotein,68-68 that differ only in amino acid composition. It may be conceived as oligosaccharide 12 having an extension of /3GlcNAc(l— N)Asn-Gly-Thr. The 500-MHz, H-n.m.r. spectrum of 13 is given in Fig. 13a, and the n.m.r. parameters are shown in Table V. 

Changes in Amino Acid Composition Following Alkaline Borohydride Treatment of the Glycopeptide... 

Amino acid analyses were performed on the glycopeptide preparation following hydrolysis of the polymer(s) in 6 N HCl for 22 hr. Approximately 38% of the amino acids were represented by seryl and threonyl residues (Table VI). In addition, the amino acid composition is similar to that obtained for both the extracellular and soluble "cytoplasmic" peptidophosphogalactomannans. The polypeptides contained only trace quantities of aromatic amino acyl residues, no detectable quantities of sulfur-containing amino acyl residues, and were rich in serine, threonine and alanine. 

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

A characteristic but unexplained feature of the peptide composition of all of these glycopeptides and peptido-oligosaccharides (see Table V) is the absence, or presence in traces only, of the aromatic amino acids. The presence of hydroxy-L-proline in some of these fractions might indicate that the glycopeptide components of these fractions are derived from connective-tissue components, as this... 

Pepsins and Pepsinogens.—The carbohydrate compositions and some sequences of amino-acids have been determined for glycopeptides derived from pepsinogens isolated from Japanese monkeys. Glycopeptides released by successive treatments of pepsinogen I with thermolysin and aminopeptidase contained 2-amino-... 

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