title: The covalent linkage of protein to carbohydrate in the extracellular protein-polysaccharide from the red alga Porphyridium cruentum.
abstract: The extracellular anionic polysaccharide isolated from cultures of a unicellular red alga, Porphyridium cruentum, contains a small amount of protein after extensive purification. The polysaccharide and protein are recovered in the same fraction after isopycnic CsCl-density-gradient centrifugation in 4M-guanidinium chloride, under conditions designed to separate proteins from polysaccharide. The peptide portion of the protein-polysaccharide is released from the polysaccharide by alkali under conditions for beta-elimination. The released peptide is non-diffusible, but in can be separated from the polysaccharide by precipitation of the polysaccharide as the cetylpyridinium complex. Under conditions for beta-elimination of certain O-glycosidic carbohydrate-protein linkages, selective destruction of serine and threonine occurs. The addition of a reducing agent to the alkali mixture produces a selective increase in alanine and alpha-aminobutyric acid. Addition of a tritiated reducing agent to the alkali mixture produces radioactive alanine and alpha-aminobutyric acid, and xylitol as the only sugar alcohol. Similar results are obtained from glycopeptides isolated from partial acid hydrolysates. A macromolecular structure of the protein-polysaccharide is suggested by a comparison of the intrinsic viscosity of material before and after treatment with alkali and proteolytic enzymes.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D002500:Centrifugation, Isopycnic; D005110:Extracellular Space / Q000378:metabolism*; D011485:Protein Binding; D011509:Proteoglycans / Q000378:metabolism*; D000461:Rhodophyta / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014994:Xylose / Q000378:metabolism
chemical_list: D000596:Amino Acids; D011509:Proteoglycans; D013912:Threonine; D012694:Serine; D014994:Xylose