Apparent heterogeneity of bovine -lactalbumin A and B in DEAE-Sephadex chromatography

Porcine alpha-lactalbumin A and B

The occurrence of the 'whey' protein, alpha-lactalbumin, in pig (Sus scrofus) milk samples from 904 sows is examined. A semi-discontinuous buffer system has been developed to detect the existence of genetic polymorphism. There are two homozygous variants, designated A and B. Both variants are isolated and it is shown by peptide and sequencing studies that the A variant differs from the B variant by having an Arg residue substituted for the Lys residue at the N-terminus of the molecule. The sequence of the first thirty residues is determined and compared with those of related alpha-lactalbumins.

Comparative aspects of milk proteins

The current status of knowledge of the major proteins of milks of various species is evaluated. Most of the non-bovine milk proteins are homologous with the recognized families of those of Bos taurus, alpha S1-caseins, alpha S2-caseins, beta-caseins, kappa-caseins, beta-lactoglobulins, and alpha-lactalbumins, each family representing a separate genetic locus specific to the mammary gland. No prominent milk protein not homologous to one of these families has yet been discovered in milk of any species. Genetic polymorphism resulting from substitutions in the polypeptide chains and various degrees of post-translational phosphorylation, glycosylation, and proteolysis have been identified in milk proteins of several species. Total protein production ranges among species from about 0.5 to 10 g/d per kg0.75 maternal weight. Proportions of the several proteins vary greatly among species, but few accurate analytical data are available except for total casein and total whey protein contents.

Purification and characterization of rat alpha-lactalbumins: apparent genetic variants

Rat alpha-lactalbumin, from the milk of Fischer 344 (CDF) rats, was isolated and purified by a combination of gel filtration and diethylaminoethyl-cellulose ion exchange chromatography. Three electrophoretically distinct proteins had alpha-lactalbumin activity. Staining for carbohydrate indicated that at least two of the three forms were glycoproteins. The low molecular weight protein fraction from the wheys of two additional strains of laboratory rat were compared to ascertain whether the composition of this fraction was common in the divergent strains. Outbred Wistar and Long-Evans dams yielded wheys containing up to six forms of alpha-lactalbumin. Either one or both of two groups of three alpha-lactalbumins were in a given milk sample. The two groups of three alpha-lactalbumins appear to represent two genetic variants upon which is imposed a polymorphic character. All forms of alpha-lactalbumin, within and between strains, were immunologically identical.

Heterogeneity in alpha-lactalbumins. I. Human alpha-lactalbumin

alpha-Lactalbumin from human milk shows an heterogeneous behaviour when subjected to ion exchange chromatography with DEAE-Sephadex. Two components have been separated, showing identical patterns in the following studies: amino acid compositions, fluorescence and circular dichroism spectra, transition temperature of denaturation, antigenicity, lactose synthase specifying activity and hydrodynamic properties. After rechromatography of either peak, these two components appeared to be in equilibrium. This equilibrium varies with the temperature and the pH of chromatography. Moreover, an increase of n-alcohol concentration in the eluting buffer also induces an increase of the second protein peak eluting at higher ionic strength. These two peaks seem to be the result of some conformational change induced upon the binding of the protein to the solid anionic matrix.