Glycopeptides fractionation

CHARACTERISTIC GLYCOPEPTIDE FRACTION OF NATURAL MICROBUBBLE SURFACTANT... 

Subsequent experimental work in this laboratory was aimed at the systematic development of an efficient method for isolating the proteinaceous surfactants, which help stabilize natural microbubbles, from both commercial agarose powder and from forest soil samples collected locally. Successful isolation of this glycopeptide fraction was eventually achieved (ref. 322), and the results obtained from an extended program of chemical analysis, to further characterize and compare chemically these proteinaceous surfactants from both natural substances, are described below. 

REVIEW OF NATURAL-PRODUCT LITERATURE AND POSSIBLE ANIMAL SOURCES OF THE GLYCOPEPTIDE FRACTION OF MICROBUBBLE SURFACTANT... 

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. 

Probable biological source of the glycopeptide fraction of microbubble surfactant... 

Despite the relatively small weight contribution of the glycopeptide fraction to the microbubble surfactant complex, this fraction has continually been found (ref. 322) to represent a reliable and characteristic component of microbubble surfactant... 

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).

Attempts to Detect Mannose-6-Phosphate in B-Galactosidase and Inhibitor Glycopeptides. Although colorimetric analysis of the inhibitor glycopeptide fraction for phosphate proved negative, the occurrence of trace quantities of mannose phosphate could not be eliminated. Experiments were therefore undertaken to demonstrate the possible presence of small amounts of mannose-6-phosphate in B-galactosidase and in the inhibitor glycopeptide fraction. 

Kalhnteri, P., Papadimitriou, E., and Antimisiaris, S. G., (2001), Uptake of hposomes which incorporate a glycopeptide fraction of asialofetuin by HepG2 cells, / Lipos. Res., 11,175-193. 

Kim and coworkers examined glycopeptides from normal, and cancerous, colonic mucosa.869 Pronase digestion of disrupted cell-membranes gave a soluble glycopeptide fraction. The fractions obtained from normal tissues inhibited Dolichos biflorus, but not Ricinus communis, hemagglutination, whereas the reverse was true of fractions obtained from malignant, colonic mucosa. No further analysis was carried out.869... 

Glycopeptide fractions isolated from developing brain contain a glucose polymer, which rapidly decreases during development [66]. It is not known whether it represents a true glycoprotein constituent. 

Whole rat brain on digestion with proteolytic enzymes releases an N-glycosidic glycopeptide fraction which has been purified using immobilized concanavalin One of the glycopeptides has an unusual sugar sequence (19) that has been shown to be part of the determinant of the so-called X-antigen. 

But such materials do possess potential antitumor activity, as ] own by the observation that certain lipid fr ions from group A streptococci and from trypanosomes (cruzi and lewlsi) exert an inhibitory effect on the growth of Ehrlich ascites and sarcoma 180 cells in mice. Indications are that it is the free fatty acids and monoglyceride components of these fractions which account for the observed activity. A glycopeptide fraction, isolated from bovine liver, s also reported markedly effective against the Ehrlich ascites tumor in vivo. ... 

A previously unknown sialic acid was found in two glycopeptide fractions isolated from the Cuvierian tubules of the sea cucumber, Holothuria forskali. It is resistant to enzymic cleavage by neuraminidase, even after mild alkaline hydrolysis for the removal of O-acyl residues however it is readily released by mild acid hydrolysis. Its chromatographic properties differ from other known sialic acids, but presumably the new species possesses neuraminic acid as its basic structure (Isemura a/., 1973). See Chapter 1. 

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