Structure of lactose

Knoop, E. and Samhammer, E. 1962. Roentgenographic studies on the crystal structure of lactose in milk powder. Milchuiissenschaft 17, 128-131. 

Exercise 20-13 Show how the structure of lactose may be deduced from the following ... 

How is lactose made in mothers milk What is unusual about the subunit structure of lactose synthase ... 

Fig. 11 (a) Structure of galactosylated chitosan. Figure reproduced with permission from [102], 1996 Elsevier, (b) Structure of lactose conjugated chitosan. Figure reproduced with permission from [134], 2006 American Chemical Society... 

Ramakrishnan, B. and Qasba, P.K. 2001. Crystal structure of lactose synthase reveals a large conformational change in its catalytic component, the beta-1,4-galactosyltransferase-I. JMol Biol 310(1) 205—218. 

The structure of lactose was, therefore, firmly established as i-O-fi-n-galactopyranosyl-D-glucopyranose (5). 

X-ray crystal structure of lactose bound to galectin 2. Dashed lines indicate hydrogen bonds. (Adapted with permission from [178])... 

Selkirk AB, Ganderton D. Influence of wet and dry granulation methods on the pore structure of lactose tablets. J Pharm Pharmacol 1970 22 86S-94S. 

The structure of lactose permease has been determined (Figure 13.11). As expected from the sequence analysis, this structure consists of two halves, each of which comprises six membrane-spanning a helices. Someot these helices are somewhat irregular. The two halves are well separated and are joined by a single stretch of polypeptide. In this structure, the sugar lies in a pocket in tlie center of the protein and is accessible from a path leads from the interior of the cell. On the basis of these structures and a wide range of other experiments, a mechanism for symporter action has been... 

Figure 13-11 Structure of lactose permease with a bound lactose analog. The amino-terminal half of the protein is shown in blue and the carboxyl-terminal half in red. (A) Side view. (B) Bottom view (from inside the cell). Notice that the structure consists of two halves that surround the sugar and are linked to one another by only a single stretch of polypeptide. [Drawn from IPVZpdb.]...

However, it has to be pointed out that it is only an approximate calculation, because we did not consider intermolecular hydrogen bonds which surely also make the structure of lactose more rigid. In such a case the activation energy of the slower secondary relaxation should be comparable to that for the y-relaxation (Ea=44 kJ/mol). This may imply that the slower secondary relaxation seen in lactose may be undetectable in the case of acethyl derivative of this disaccharide, because maxima of both secondary relaxations can be too close to each other. In fact, the inspection of the dielectric loss spectra obtained for octa-0-acetyI-Iactose below its glass transition temperature (see Fig. 2) showed that there is only one secondary relaxation peak. However, a detailed analysis of the y- loss peak revealed that probably two secondary processes contribute to it. 

Outline the metabolism of lactose in E. coli. Draw the structure of lactose, describe its entry into the cell, and write the equations for the reactions catalyzed by j3-gaIactosidase, providing both the substrates and the products. 

You can find a good conformational picture of (3-D-galactose on page 1146 of the textbook, as the left-hand part of the structure of lactose. Switch stereochemistry at Cl for the a isomer. Notice in the answer below how the name, 3-(a-D-galactopyranos-l-yl)- (J-D-galactopyranose. translates into the structure ... 

Figure 7.10 The structures of lactose and lactitol mono-ester surfactants. The asterisks denote alternative locations for the fatty acid substitution.

Show how the following experimental evidence can be used to deduce the structure of lactose (Section 22.12D) ... 

Draw the structure of lactose. Label the glucose and galactose rings in this disaccharide. 

FIGURE 22.61 The issues that must be addressed to determine the structure of (+)-lactose. 

We now need to know three details about the dimeric structure of lactose (Fig. 22.61). The issues are ... 

Scheme 2. Chemical structure of lactose aryl diazirine (R=H)...

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