Galactoside transport

Answer Treat a suspension of the bacteria as follows Add lactose at a concentration well above the A), so that virtually every molecule of galactoside transporter binds lactose. Next, add nonradiolabeled NEM and allow it to react with all available —SH groups on the cell surface. Remove excess lactose by centrifuging and resuspending the cells, then add radiolabeled NEM. The only Cys residues now available to react with NEM are those in the transporter protein. Dissolve the membrane proteins in sodium dodecylsulfate (SDS), and separate them on the basis of size by SDS gel electrophoresis. The Mt of the labeled band should represent that of the galactoside transporter. 

H.R. Kaback, E. Bibi, and P.D. Roepe. 1990. P-Galactoside transport in E. coir. A functional dissection of lac permease Trends Biochem. Sci. 8 309-314. (PubMed)... 

Thus, /3-galactoside transport is coupled to an exergonic system providing 4132 cal/mole. 

The y gene codes for M protein, a protein associated with the P-galactoside transport system. This protein was formerly called galactoside permease, but that term has now been reserved to indicate the entire transport system. The mechanism of transport which facilitates entry of /S-galactosides into the cell has been reviewed by Kennedy [83] and Kepes [84]. The permease system has the ability to allow induced cells to concentrate galactosides 100-fold over their concentration in the external medium and requires the presence of a supply of unsaturated fatty acids for activity [84a]. 

S-Galactosidase ehymotrypsin, 155 /3-Galactoside, transport of, 67 /3-D-Galactosylamine, synthesis of, 363 Galactosylgalactosidase, 27... 

Upon induction of the lac system, the synthesis of phospho-/ -galac-tosidase activity and galactoside transport activity increase coordinately. In... 

The interpretation of these experiments is complicated by the subsequent report of Linden and Fox that 5-galactoside transport gives two inflections in Arrhenius plots, even when the mutant is grown on a single fatty acid. In fact, oleate-grown cells have inflections at 12.8°C and 22°C which are very similar to the 14.6°C and 26°C inflections claimed for cells grown on elaidate and switched briefly to oleate. 

In bacteria, accumulation of substrates against a concentration gradient can occur through two main classes of transport systems (see [30] for a summary). The prototype of the first class of transporters is the /3-galactoside permease of Escherichia coli (see [31]). It is a relatively simple system involving only a single membrane-bound protein. It catalyzes a lactose-H symport. Other transporters... 

The Y gene, which encodes a galactoside permease, the transport protein required for entry of lactose into the cell... 

Kennedy, E. P. and Scarborough, G. A. 1967. Mechanism of hydrolysis of O-nitrophenyl-d-galactoside in Staphylococcus aureus and its significance for theories of sugar transport. Proc. Natl. Acad. Sci. USA 58, 225-228. 

The Permease Systems of Bacteria. The best defined of these is the galactoside permease of E. coli. This transport system mediates the active accumulation of galactosides in the presence of metabolic energy and the facilitated diffusion of these compounds when the energy system is blocked (8). A specific galactoside-binding protein has been implicated, but it seems clear that the system is different from the phosphotransferase system described above since no covalent intermediates of... 

The bacterial lactose-transport protein (lactose permease) transports j3-galactosides, such as lactose, o-nitrophenyl-jS-galactoside, and isopropyl-jS-thiogalactoside. It does not transport galactosides with an a-glycosidic linkage. 

In bacteria, Na+ is often replaced by H+ as the carrier of nutrients. The best known mechanisms of this sort are the various galactoside (e.g., lactose) transporters, because lactose is an important carbon source for many bacteria. The work that can be performed (e.g., in transporting a nutrient) by generating a proton gradient across membranes may be expressed by the following, which encompasses both the chemical component (concentration gradient) and the electrical component in the form of the membrane potential AW ... 

A crucial clue to the mechanism of gene regulation was the observation that two other proteins are synthesized in concert with P-galactosidase—namely, galactoside permease and thiogalactoside transacetylase. The permease is required for the transport of lactose across the bacterial cell membrane. The transacetylase is not essential for lactose metabolism but appears to play a role in the detoxification of compounds that also may be transported by the permease. Thus, the... 

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