Isolation and properties of -lactalbumin from various sources

Structure and properties of avian small heat shock protein with molecular weight 25 kDa

The primary structure of chicken small heat shock protein (sHsp) with apparent molecular weight 25 kDa was refined and it was shown that this protein has conservative primary structure 74RALSRQLSSG(83) at Ser77 and Ser81, which are potential sites of phosphorylation. Recombinant wild-type chicken Hsp25, its three mutants, 1D (S15D), 2D (S77D+S81D) and 3D (S15D+S77D+S81D), as well as delR mutant with the primary structure 74RALS-ELSSG(82) at potential sites of phosphorylation were expressed and purified. It has been shown that the avian tissues contain three forms of Hsp25 having pI values similar to that of the wild-type protein, 1D and 2D mutants that presumably correspond to nonphosphorylated, mono- and di-phosphorylated forms of Hsp25. Recombinant wild-type protein, its 1D mutant and Hsp25, isolated from chicken gizzard, form stable high molecular weight oligomeric complexes. The delR, 2D and 3D mutants tend to dissociate and exist in the form of a mixture of high and low molecular weight oligomers. Point mutations mimicking phoshorylation decrease chaperone activity of Hsp25 measured by reduction of dithiothreitol induced aggregation of alpha-lactalbumin, but increase the chaperone activity of Hsp25 measured by heat induced aggregation of alcohol dehydrogenase. It is concluded that avian Hsp25 has a more stable quaternary structure than its mammalian counterparts and mutations mimicking phosphorylation differently affect chaperone activity of avian Hsp25, depending on the nature of target protein and the way of denaturing.

Pituitary-induced lactation in mammary gland explants from the pregnant tammar (Macropus eugenii): a negative role for cyclic AMP

1. alpha-Lactalbumin and casein have been isolated from tammar milk. 2. alpha-Lactalbumin was induced in mammary explants by culture with anterior pituitary. 3. Casein was induced maximally in the presence of a physiological concentration of prolactin alone. 4. Progesterone did not inhibit the prolactin-induced synthesis of casein, alpha-lactalbumin, galactosyltransferase or fatty acids. 5. Both dibutyryl cAMP and a combination of cholera toxin and IBMX did significantly inhibit the induction of casein and alpha-lactalbumin. 6. Progesterone withdrawal is not a component of the lactogenic trigger in this marsupial but cAMP may be a common intracellular signal for negative control of lactogenesis in both marsupials and eutherians.

Validation of radioimmunoassay for human lactalbumin in the serum by testing the endogenous antibodies interference

For re-establishing the value of human lactalbumin as a functional marker of normal and pathological activity of the breast a sensitive and specific radioimmunoassay was established with the prior important control of the interference of endogenous antibodies. The specificity of the assay was assessed by the absence of interference from other proteins in milk or in breast cyst fluid, various hormones and tumor markers. Bovine lactalbumin showed incomplete and weak cross-reactivity. By an enzymoimmunoassay method it was shown that all the 222 human sera studied contain IgG immunoglobulins which bind bovine and human lactalbumin with greater reactivity of children's serum and without relationship to the blood groups. The maximum affinity constant of these endogenous immunoglobulins determined by the radioimmunoassay method is 4.5 times greater for bovine (Kd = 18 X 4(-11) M) than for human (Kd = 4 X 10(-11) M) lactalbumin. These endogenous anti-lactalbumin immunoglobulins caused no interference in the radioimmunoassay as shown by the complete correlation between the concentrations of human lactalbumin previously incubated and added to sera containing high-affinity antibodies and those measured directly in the radioimmunoassay. This lack of interference was explained by the higher (22-fold) affinity constant of the rabbit antiserum against human lactalbumin (Kd = 9 X 10(-12) M). The study of endogenous antibodies by the two enzymes and radioimmunoassay methods is needed before assessing and using a radioimmunoassay of human lactalbumin in serum.

Alpha-Lactalbumin and lactose concentrations in rat milk during lactation

Homogeneous rat alpha-lactalbumin was prepared from whey by chromatography on DEAE-Sephadex A-50 and Ultrogel AcA 44. Two biologically active forms of alpha-lactalbumin were apparent after ion-exchange chromatography, but on gel filtration the combined forms were eluted as a single peak with a molecular weight of approx. 33000. The molecular weight when determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis was 15100. Antiserum to alpha-lactalbumin was prepared from rabbits, and single radial immunodiffusion was used to measure the concentration of alpha-lactalbumin in milk expressed from rats during lactation and for 2 days after the cessation of lactation. A significant positive correlation (r = + 0.89) between the concentrations of alpha-lactalbumin and lactose was obtained for the first 20 days of lactation. This is consistent with the suggestion that alpha-lactalbumin may control the concentration of lactose in milk. However, a significant negative correlation (r = -0.91) between the concentration of alpha-lactalbumin and lactose was obtained for 2 days after the cessation of lactation on day 20.

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.

Characterization of major milk proteins from BALB/c and C3H mice

Milk proteins from BALB/c and C3H mice were characterized with respect to their electrophoretic migration in polyacrylamide gels under alkaline and acid conditions. The major casein and whey proteins from each strain migrated similarly under the conditions employed. Phosphoproteins were identified by staining with "Stains-all" and by changes in electrophoretic mobility and staining induced by prior treatment with phosphatase. Sialic acid-rich glycoproteins were identified by staining with periodic acid-Schiff and with "Stains-all" by prior treatment with neuraminidase to identify sialic acid as the acidic portion of the molecule. The two major whey proteins were characterized further by their migration in sodium dodecyl sulfate gels. One protein had the same mobility as mouse serum albumin. The other protein migrated with a mobility similar to that of bovine alpha-lactalbumin. The identity of the former protein was confirmed by its reaction with goat anti-mouse serum albumin in an immunodiffusion procedure, and the latter protein by its B protein activity in the lactose synthetase assay.

Isolation, composition and functional properties of alpha-lactalbumins from several species

1. Galactosyltranferases were isolated from bovine and pig milk and alpha-labtalbumins from milks of cow, pig, dog, rabbit, baboon and chimpanzee. 2. Alpha-Lactalbumins were characterized by gel electrophoresis, amino acid composition, ultraviolet absorbance, and ability to promote synthesis of lactose by the galactosyltransferases. 3. The order of K-m values of the various alpha-lactalbumins was the same with both cow and pig galactosyltransferases and differed from the order predicted from taxonomical classification of the species. 4. A280/A260 abosrbance ratios were correlated with K-m values suggesting involvement of tyrosyl groups in the function of alpha-lactalbumin.

Immunological cross-reactions of alpha-lactalbumins from different species

Four rabbit antibodies have been prepared, which are specifically directed against alpha-lactalbumins from different sources; namely human, cow, goat and sheep milk. Each of these antibodies was tested for its ability to react with, separately, each of the four proteins. The immunological reactions were assessed by means of different techniques: double immunodiffusion in agar gel as well as affinity chromatography of antibodies, using antigens covalently bound to an insoluble matrix. In each case, the strongest reaction was observed between homologous antibody and (matrix-bound) antigen; heterologous antigens were, however, also capable of cross-reaction. Whereas no cross-reaction between human alpha-lactalbumin and antibodies against the bovine protein could be evidenced by immunodiffusion, the occurrence of soluble complexes has been disclosed by means of a gel filtration technique.