Glycomics is emerging as a new field for the biology of complex glycoproteins and glycoconjugates. The lack of versatile glycanlabeling methods has presented a major obstacle to visualizing at the cellular level and studying glycoconjugates.

Seven kinds of ripened cheeses (8-mo-aged and 24-mo-aged Gouda, Emmental, Blue, Camembert, Edam, and Havarti) were homogenized with distilled water, and water-soluble peptides were prepared by C-18 hydrophobic chromatography. The inhibitory activity to angiotensin I-converting enzyme and decrease in the systolic blood pressure in spontaneously hypertensive rats were measured before and after oral administration of each peptide sample. The strongest depressive effect in the systolic blood pressure (-24.7 mm Hg) and intensive inhibitory activity to angiotensin I-converting enzyme (75.7%) were detected in the peptides from 8-mo-aged Gouda cheese. Four peptides were isolated by HPLC with reverse-phase and gel filtration modes. Their chemical structures and origins, clarified by combination analyses of protein sequencing, amino acid composition, and mass spectrometry, were as follows: peptide A, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln [alpha(s1)-casein (CN), B-8P; f 1-9]; peptide B, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln-Gly-Leu-Pro-Gln (alpha(s1)-CN, B-8P; f 1-13); peptide F, Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-Asn (beta-CN, A2-5P; f 60-68); and peptide G, Met-Pro-Phe-Pro-Lys-Tyr-Pro-Val-Gln-Pro-Phe (beta-CN, A2-5P; f 109-119). Peptides A and F, which were chemically synthesized, showed potent angiotensin I-converting enzyme inhibitory activity with little antihypertensive effects.

Whey protein was digested with one of seven kinds of proteases at 37 degrees C (trypsin, proteinase K, actinase E, thermolysin, or papain) or at 25 degrees C (pepsin or chymotrypsin) for 24 h. The digested samples were assayed for the inhibitory activity of angiotensin-converting enzyme and for changes in the systolic blood pressure caused in spontaneously hypertensive rats after gastric intubation. The strongest depressive effect on the systolic blood pressure (-55 mm Hg) was observed at 6 h after gastric intubation of the whey protein that was digested by proteinase K. Finally, six peptides were chromatographically isolated from the proteinase K digest by a combination of hydrophobic reversed-phase HPLC and gel filtration. The amino acid sequences and their origins were clarified as follows: Val-Tyr-Pro-Phe-Pro-Gly [beta-casein (CN); f 59-64], Gly-Lys-Pro (beta 2-microglobulin; f 18-20), Ile-Pro-Ala (beta-lactoglobulin; f 78-80), Phe-Pro (serum albumin; f 221-222; beta-CN, f 62-63, f 157-158, and f 205-206), Val-Tyr-Pro (beta-CN; f 59-61), and Thr-Pro-Val-Val-Val-Pro-Pro-Phe-Leu-Gln-Pro (beta-CN; f 80-90). Chemical synthesis of these six peptides confirmed that all peptides, except an undecapeptide, have antihypertensive activity in spontaneously hypertensive rats. The synthetic tripeptide Ile-Pro-Ala, originating from beta-lactoglobulin, showed the strongest antihypertensive activity (-31 mm Hg).

No abstract

The variation and distribution of O-glycosidically linked sugar chains in kappa-casein from bovine mature milk were analyzed by HPLC, fast atom bombardment mass spectrometry, and 13C nuclear magnetic resonance. A monosaccharide alditol (N-acetylgalactosaminitol) and four oligosaccharide alditols [a neutral disaccharide (galactosyl-beta 1-3N-acetylgalactosaminitol), two acidic trisaccharides (straight chain: N-acetylneuraminyl alpha 2-3galactosyl-beta 1-3N-acetylgalactosaminitol and branch chain: galactosyl beta 1-3(N-acetylneuraminyl alpha 2-6)N-acetylgalactosaminitol), and an acidic tetrasaccharide(N-acetylneuraminyl alpha 2-3galactosyl-beta 1-3(N-acetylgalactosaminyl alpha 2-6)N-acetylgalactosaminitol] were identified as sugar chains linking on normal bovine kappa-casein. The most dominant sugar chain was an acidic tetrasaccharide. The four oligosaccharide chains were identical to those already found, but N-acetylgalactosamine was a newly identified sugar chain linking on kappa-casein. The distribution of monosaccharide, disaccharide, trisaccharide (straight), trisaccharide (branched), and tetrasaccharide chains were determined by HPLC to be .8, 6.3, 18.4, 18.5, and 56.0%, respectively (means of five kappa-caseins).