Blood group substances, amino acids

These bacterial antigens (in their susceptibility to hydrolysis, which separates polysaccharide from the rest of the molecular complex) differ markedly from the blood-group substances, where amino acids and sugars cannot be separated from one another as polypeptide and polysaccharide. ... 

Gastric secretion represents a very complex naixture of electrolytes, water, carbohydrates, proteins, peptides, and amino acids, which are partly in solution and partly in more or less stable suspension. The large molecular materials of gastric secretion include enzymes, mucosubstances, serum proteins, peptides and products of proteolytic degradation of gastric proteins and mucoproteins, and blood group substances. 

Elementary analysis of B substance (G4) showed 41% carbon, 6.6% hydrogen, 5.7% nitrogen, and 7% acetyl. The same sugars and amino sugars were again found, including 17.9% fucose, as well as the same 11 amino acids. However, content of hexosamine was lower (20-22% only) as compared to 33-37% in blood group substances A, H, and Le. ... 

Blood group substance H (A8) designated in the early literature by O, contained 41.4% carbon, 6.9% hydrogen, 5.3% nitrogen, and 8.7% acetyl. Its fucose content was 14% and that of hexosamine 31%. The same 11 amino acids were present. Le substance showed 41.5% carbon. 

Buffers resist changes in pH. Substances can act as buffers at their pK values. In proteins, the amino acids with ionizable R-groups can act as buffers, altiiough the only amino acid that is useful in maintaining physiologic pH (7.2-7.4) is histidine with an R-group pK near 7. Hemoglobin can act as an intracellular buffer in red blood cells because it contains histidyi residues. 

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