title: Characterization of the protein profile of donkey's milk whey fraction.
abstract: Characterization of the protein profile of the whey fraction from a milk sample taken from an individual donkey belonging to the 'Ragusana' species of the East of Sicily is reported. Direct RP-HPLC/electrospray ionization (ESI)-MS analysis of the whey fraction allowed the detection of some unknown components, together with the identification of already known whey proteins. Matrix-assisted laser desorption/ionization (MALDI)-TOF/MS and RP-HPLC/ESI-MS/MS analysis of the enzymatic digests of the unknown components resulted the identification and characterization of (1) two beta-casein fragments; (2) the sequence of donkey's serum albumin; and (3) the oxidized methionine forms of lysozyme B and alpha-lactoalbumin. One of the two beta-casein fragments corresponds to the sequence Val(176)-Arg(189) of the horse's beta-casein. The second one corresponds the C-terminal sequence Tyr(199)-Val(226) of the horse's beta-casein, with four amino acid substitutions (Q --> R(203), L/I --> P(206), F --> L(210) and P --> A(219)). Both fragments, reasonably arising by endogenous proteases cleavage of the donkey's beta-casein, could be potential biologically active peptides. Direct mass spectrometric sequence characterization of the detected donkey's serum albumin reveals the presence of the amino acid substitution Val --> Ile at position 497 with respect to the cDNA deduced sequence. The oxidized forms of lysozyme B and alpha-lactoalbumin are selectively oxidized at methionine 79 and methionine 90, respectively.
authors.affiliation: Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A Doria, 6, I-95125, Catania, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cunsolo
authors.forename: Rosaria
authors.initials: R
authors.lastname: Saletti
authors.forename: Vera
authors.initials: V
authors.lastname: Muccilli
authors.forename: Salvatore
authors.initials: S
authors.lastname: Foti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018397:Equidae; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000032:analysis*; D008969:Molecular Sequence Data; D020543:Proteome / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000067816:Whey Proteins
chemical_list: D008894:Milk Proteins; D020543:Proteome; D000067816:Whey Proteins