Characterization of APMCG-1
The chemical composition of APMCG-1 was analyzed and the following
contains were observed: 0.85% alkaloids, 25.98% amino acids and
peptides, 39.8% carbohydrates, 0.95% flavonoids, 0.3% polyphenols,
1.47% saponins, 15% uronic acids, and 15.63% unknown (Fig. 6A). To
identify the presence or absence of glycopeptides in APMCG-1, we used
β-elimination reaction. The results showed that the absorption value of
the UV spectrum of APMCG-1 significantly increased at 240 nm after
alkali treatment, and contained O-linked glycopeptide bonds (Fig. 6B).
The results of thin-layer chromatography analysis showed that APMCG-1
also contained sugars and peptides. As revealed by the FT-IR spectrum,
the strong and broad absorption peak at around 3400
cm-1 indicated the stretching vibration peak of -OH or
-NH on the polysaccharide. The moderate-intensity absorption peak at
2920 cm-1 marked the stretching vibration peak of
-CH2 and -CH. The absorption peaks at 1600
cm-1 implied the asymmetric stretching vibration peaks
caused by C=O. The above absorption peaks were characteristics of
polysaccharides. The absorption peak at 1400 cm-1 was
caused by the deprotonated carboxyl group, indicating the presence of a
uronic acid structure. The absorption peak at 760 cm-1represented the absorption peak of pyran-ring symmetric ring stretching
vibration, revealing the presence of pyran polysaccharide (Fig. 6C). The
retention times of mannose, rhamnose, glucuronic acid, galacturonic
acid, glucose, xylose, galactose, and fucose were observed at 13.120,
16.678, 21.075, 25.187, 30.560, 34.898, 35.640, 38.224 and 42.174 min,
respectively. The ratio of monosaccharide of APMCG-1 was mannose,
rhamnose, galacturonic acid, glucose, xylose, galactose and arabinose
1:2.57:15:24.54:3.4:28.54:12.38 (Fig. 6D). Amino acid involving cysteic
acid, methionine alum, aspartic acid, threonine, serine), glutamate,
glycine, alanine, cysteine, valine), methionine, isoleucine, leucine,
tyrosine, phenylalanine, histidine, lysine, arginine and proline were
used as the standard substance, the amino acid composition of APMCG-1
was composed of aspartic acid (2.797%), methionine (3.271%),
phenylalanine (6.503%), histidine (4.748%), arginine (2.513%),
proline (1.433%), and NH4 (9.086%) (Fig. 6E). These findings denote
that APMCG-1 is an active glycopeptide isolated from MCG.