Lactose-protein complexes

Several of these geometries correspond to right-handed helices with between 2 and 3 residues per turn, but most lead to left-handed cellulosic structures. Further, this same majority has a distribution of positions that is very similar to that of the small molecule conformations and the conformations in the protein cellodextrin complexes. Whether the lactose-protein complexes are less accurately determined or there are special causes for the wider spread of the data is under study as this is written. 

We do not know why the lactose-protein complex structures have a much wider range of conformations. At this time we cannot say that they are less accurately determined than the complexes of proteins and cellodextrins. 

Figure 15-14. A QM MM3 hybrid energy surface for cellobiose (see text). The dielectric constant was set to 3.5, reducing the strength of the hydrogen bond in the water dimer to about 2.35kcal/mol each. Plotted in the tp,t space are the conformations of all of the above crystal structures except the lactose-protein complexes...

Figure 15-15. The same energy surface as in 15-13, but with the lactose-protein complexes plotted instead...

This enzyme [EC 2.4.1.22] is a protein complex of two proteins (designated A and B) and catalyzes the reaction of UDP-galactose with D-glucose to generate UDP and lactose. In the absence of the ce-lactalbumin (protein B), the enzyme catalyzes the transfer of galactose from UDP-galactose to A-acetylglucosamine (Le., the activity of A-acetyllactosamine synthase, EC 2.4.1.90). 

Sequencing gel electrophoresis patterns of DNA fragments irradiated in presence of bound proteins reveal regions in which no FSB are occurring. They are called protein "radiolytic footprints" on DNA [15]. Such protected regions were observed when irradiating the operator-lactose repressor complexes (see Inset 1). 

Figure 15-12 shows the distribution of the geometries of lactose moieties from protein complexes. There is a much wider range of these structures (notice the difference in values on the axes), although most are in the same location as the above small-molecule and protein complex structures. 

Figure 15-12. The locations in (p, / space of the conformations of the lactose linkages in protein complexes along with the approximate iso- and iso-/z contours from Figure 15-6...

Lactose Synthases.—2-Diazoacetamido-2-deoxy-D-glucose accepted theD-galacto-syl residue transferred in a reaction catalysed by lactose synthase. Physicochemical studies suggested that the amino-sugar derivative makes contact with the A protein, rather than with a-lactalbumin, in the lactose synthase complex. 

Kato, Y., Matsuda, T., Kato, N. and Nakamura, R. Andysis of lactose-protein Maillard complexes in commercial milk products by using the specific monoclonal antibody. In Maillard reaction in Chemistry, Food and Health. Labuza, T. P. and Reineccius, G. A. Eds., Birkhauser Verlag, Basel, Boston, Berlin, 1995, ppl88-194. 

Ice cream serves as a wonderful (and tasty) example of a complex, dynamically heterogeneous food system. A typical ice cream mix contains milk or cream (water, lactose, casein and whey proteins, lipids, vitamins, and minerals), sucrose, stabilizers and emulsifiers, and some type of flavor (e.g., vanilla). After the ingredients are combined, the mix is pasteurized and homogenized. Homogenization creates an oil-in-water emulsion, consisting of millions of tiny droplets of milk fat dispersed in the water phase, each surrounded by a layer of proteins and emulsifiers. The sucrose is dissolved in... 

Fig. 7 Comparison of experimental and predicted STD values from CORCEMA-ST protocol for the crystal structure of sialoadhesin-sialyl lactose complex at protein/ligand ratio of 1 300. Reprinted from [63] 2004, with permission from Elsevier...

Milk is a remarkably complex biological fliud. It contains several hundred different molecules including enzymes and also different cells, e.g. inunune cells. In particular, it contains proteins, fat, lactose, both the indispensable and dispensable amino acids, essential fatty acids, micronutrients, cholesterol and phospholipids. Milk is essential for the first four months of life. The major protein in milk is... 

The Steffen process, which uses calcium oxide for precipitation of sucrose from molasses, has been applied to the recovery of lactose from cheese whey (Cerbulis 1973). By proper control of the reaction, over 90% of the lactose can be recovered as an insoluble calcium-lactose complex. The addition of ferric chloride in combination with calcium oxide improves lactose yields. Addition of equal volumes of acetone or methanol gives almost complete precipitation of lactose and protein from whey. 

Ivatt, R. J. and Rosemeyer, M. A. 1972. The complex formed between the A and B proteins of lactose synthetase. Febs Letters 28, 195-197. 

Addition of specific compounds to milk has been used to allow spec-trophotometric measurement of lactose as the osazone (Wahba 1965) and fat by fluorescence (Bakhiren and Butov 1968 Konev and Kozlova 1970). The dye-binding method for measuring protein in milk is based on the ability of sulfonic acid dyes to complex with the basic amino acid residues of milk proteins at low pH (Fraenkel-Conrat and Cooper 1944). Dye binding correlates well with Kjeldahl (Sherbon 1970) and infrared (Mogot et al. 1982 Grappin et al. 1980) results, but variations are caused by the different compositions of the different milk proteins (Ashworth 1966 Vanderzant and Tennison 1961). 

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