Sequence analysis of Camelus dromedarius milk caseins.
Alpha s1-, alpha s2-, beta- and kappa-caseins from Somali camels (Camelus dromedarius) were purified by acid precipitation at pH 4.4, crudely separated into an alpha-CN and a beta-CN fraction and further purified by reversed-phase HPLC. Fragments of tryptic digests were sequenced. Amino acid patterns obtained were used to screen a cDNA library constructed from mRNA from lactating udder tissue. Full length clones corresponding to the four caseins were sequenced. The numbers of residues in the sequences deduced were alpha s1-CN 207, alpha s2-CN 178, beta-CN 217, kappa-CN 162. Percentage similarity to bovine proteins was alpha s1-CN A 39, alpha s2-CN 56, beta-CN 64, kappa-CN 56. Acid-precipitated casein of pooled milk was separated by reversed-phase HPLC and monitored at 220 nm, and its composition, estimated from peak integration, was (g/kg total casein) alpha s1-CN 220, alpha s2-CN 95, beta-CN 650, kappa-CN 35. Degrees of phosphorylation and glycosylation were determined by laser ionization mass spectrometry and sequence pattern analysis. Molecular masses determined were (kDa) alpha s1-CN A, 24.755 and 24.668; alpha s1-CN B, 25.293; alpha s2-CN 21.993; beta-CN, 24.900; kappa-CN 22.294-22.987. The pH values of the most probable isoelectric points were: alpha s1-CN A 6P 4.41, alpha s1-CN B 6P 4.40, alpha s2-CN 9P 4.58, beta-CN 4P 4.66, kappa-CN 1P, with ten sialic acid residues bound, 4.10.
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Laboratorium für Milchwissenschaft, Eidgenössische Technische Hochschule, Zürich, Schweiz.
Farah
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Puhan
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002162:Camelus; D002364:Caseins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D012085:Chymosin / Q000378:metabolism; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D005260:Female; D015723:Gene Library; D008892:Milk / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification; D021382:Protein Sorting Signals / Q000737:chemistry; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014357:Trypsin
D002364:Caseins; D017931:DNA Primers; D018076:DNA, Complementary; D010446:Peptide Fragments; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D014357:Trypsin; D012085:Chymosin