Lactalbumins

Albumins. Soluble proteins both in water and in dilute aqueous salt solutions found in all living tissue. Typical albumins are ovalbumin from eggs and lactalbumin from milk. 

The elution volume, F/, and therefore the partition coefficient, is a function of the size of solute molecule, ie, hydrodynamic radius, and the porosity characteristics of the size-exclusion media. A protein of higher molecular weight is not necessarily larger than one of lower molecular weight. The hydrodynamic radii can be similar, as shown in Table 4 for ovalbumin and a-lactalbumin. The molecular weights of these proteins differ by 317% their radii differ by only 121% (53). 

WJ Browne, ACT North, DC Phillips, K Brew, TC Vanaman, RC Hill. A possible three-dimensional stnicture of bovine a-lactalbumin based on that of hen s egg-white lysozyme. J Mol Biol 42 65-86, 1969. 

The details of many all-atom unfolding simulation studies have been summarized in several reviews [17,46,47]. These studies include unfolding simulations of a-lactalbumin, lysozyme, bovine pancreatic trypsin inhibitor (BPTI), barnase, apomyoglobin, [3-lacta-mase, and more. The advantage of these simulations is that they provide much more detailed information than is available from experiment. However, it should be stressed that there is still only limited evidence that the pathways and intermediates observed in the nanosecond unfolding simulations correlate with the intermediates observed in the actual experiments. 

Nitrogen sources include proteins, such as casein, zein, lactalbumin protein hydrolyzates such proteoses, peptones, peptides, and commercially available materials, such as N-Z Amine which is understood to be a casein hydrolyzate also corn steep liquor, soybean meal, gluten, cottonseed meal, fish meal, meat extracts, stick liquor, liver cake, yeast extracts and distillers solubles amino acids, urea, ammonium and nitrate salts. Such inorganic elements as sodium, potassium, calcium and magnesium and chlorides, sulfates, phosphates and combinations of these anions and cations in the form of mineral salts may be advantageously used in the fermentation. 

Grinberg, V.Y., Grinberg, N.V., Burova, T.V., Dalgalarrondo, M., and Haertle, T., Ethanol-induced conformational transitions in holo-a-lactalbumin Spectral and calorimetric studies. Biopolymers, 46(4), 253-265, 1998. 

The influence of pH, ionic strength, and protein concentration on the extraction of a-lactalbumin and 3-lactoglobulin from an aqueous solution with water/AOT/isooctane microemulsions and their separation has been reported [168],... 

The range of whey products that are used include, for example, ultra-filtered and dried WPC, which contains between 20% and 89% protein ion exchange and membrane filtered WPI, which contains at least 90-95% protein (Tunick, 2008) and other whey fraction-enriched products such as p-lactalbumin. These enriched protein whey products can be texturized and used in the manufacture of high-protein content puffed com products (Onwulata et al, 2010). 

FIGURE 5.1 Rapid molecular simulations of the apoprotein form of a-lactalbumin in vacuo, showing the native holo state and the effect of simulations at 5 and 298 K of the apoform (Farrell et ai, 2002). 

Three different whey protein products extruded at the cook temperature of 75 °C resulted in varying degrees of melt texturization (Table 5.3). Among the whey proteins, WPC (WPC80) was the least texturized. Whey lactalbumin (WLAC) and WPI were both significantly (p < 0.05) more texturized, but a wider spread of texturization was observed for WPI, the initial and final values were from 28% to 94.8%, and therefore more emphasis was placed on studying WPI (Onwulata et ah, 2006). 

WPC80 whey protein concentrate, 80% protein. WLAC whey lactalbumin. WPI whey protein isolate number reported is mean of three samples. Means with different letters within a column are significantly (p < 0.05) different. 

Gezimati, J., Creamer, L. K., and Singh, H. (1997). Heat-induced interactions and gelation of mixtures of p-lactoglobulin and a-lactalbumin. /. Agric. Food Chem. 45,1130-1136. 

These assumptions were confirmed by the electrophoresis study of the washed creams. Electrophoresis of purified fat globules is a convenient method to characterize and quantify proteins adsorbed at the oil-water interface [35]. Electrophoretic data indicate that no casein, nor whey proteins, were adsorbed at the surface of raw-milk fat globule. Upon homogenization, caseins adsorbed preferentially at the lipid-water interface. In this case, bound a-lactalbumin accounted for 16% of the total interfacial proteins. Heat treatment also induced the interaction of proteins with the fat globules. The amount of bound proteins (per mg of lipids) for heated raw milk was half that for homogenized milk. 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

Weinbrenner, W. F. and Etzel, M. R., Competitive adsorption of a-lactalbumin and bovine serum albumin to a sulfopropyl ion-exchange membrane, J. Chromatogr. A, 662, 414, 1994. 

Rush, R. S., Cohen, A. S., and Karger, B. L., Influence of column temperature on the electrophoretic behavior of myoglobin and a-lactalbumin in high-performance capillary electrophoresis, Anal. Chem., 63, 1346, 1991. 

Fig. 6. Backscattered Raman and ROA spectra of native (top pair) and A-state (second pair) bovine G -lactalbumin, and of native (third pair) and A-state (bottom pair) equine lysozyme, together with MOLSCRIPT diagrams of the crystal structures (PDB codes lhfz and 2eql) showing the tryptophans. The native proteins were in acetate buffer at pH 4.6 and 5.6, respectively, and the A-states in glycine buffer at pH 1.9. The native-state and A-state spectra were recorded at 20°C and 2°C, respectively.

Bovine a -lactalbumin (BLA) is a protein whose structure appears to be unusually malleable and, as such, has been the focus of many studies of what is termed the molten globule transition. At low pH, BLA expands and is said to lose tertiary structure, but it maintains substantial secondary structure in a partial unfolding transition (molten globule... 

Fig. 35. Far-UV (a) and near-UV (b) CD spectra of bovine Q -lactalbumin in various states. (1 and 2) The native state of the holo and apo forms, respectively (3) the A state (a) thermally unfolded state at 41° (4) and 78°C (5) (6) GdmCl-unfolded state, (b) Thermally unfolded state at 62.5°C (4) GdmCl-unfolded state (5). The open circles (holo) and squares (apo) are values derived by extrapolating refolding curves to zero time. From Kuwajima et al. (1985). Biochemistry 24, 874-881, with permission. 1985, American Chemical Society.

Fig. 36. Far-UV (upper panel) and near-UV (lower panel) CD spectra of guinea pig a-lactalbumin. Native state, pH 7 (—) A state, pH 2 ( ) unfolded state, 9 M urea, pH 2...

Fig. 37. Difference CD spectrum (native-molten globule) in bovine a-lactalbumin ( ). Derivedfrom data of Kuwajima et al (1985) for native (—) and molten globule ( ) forms. 

The near-UV CD of bovine o -lactalbumin is shown in Figure 35b. The strong CD of the native protein contrasts with the weak CD of the molten globule, which is comparable to that of the heat- and Gdm-HCl-denatured protein. The weakness of the aromatic CD bands in the molten globule is attributable to the absence of a well-defined conformation and environment for the aromatic side chains, which leads to averaging of the aromatic CD contributions over many conformations and thus to extensive cancellation. 

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