Thiogalactosides

Figure 39-2. The positional relationships of the structural and regulatory genes of the lac operon. lacZ encodes 3-galactosidase,/ocT encodes a permease, and lacA encodes a thiogalactoside transacetylase. lad encodes the lac operon repressor protein.

The A gene, which encodes a thiogalactoside transacetylase enzyme that is not essential for lactose metaboUsm and whose function is uncertain... 

Figure 4. Design of synthesis routes to methyl 3- and 4-thiogalactosides. ...

Lambda S.R.R thiogalactoside alters cell products are essential... 

The lactose (toe) operon (Fig. 28-7a) includes the genes for jS-galactosidase (Z), galactoside permease (F), and thiogalactoside transacetylase (A). The last of these enzymes appears to modify toxic galactosides to facilitate their removal from the cell. Each of the three genes is preceded by a ribosome binding site (not shown in Fig. 28-7) that independently directs the translation... 

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. 

A large number of compounds have been tested for their capacity to induce /3-galactosidase. All inducers contain an intact, unsubstituted galactosidic residue (fig. 30.4). Many compounds that are not themselves substrates for /3-galactosidase such as thiogalactosides are good inducers... 

In a cell that is lacZ, what would be the relative thiogalactoside transacetylase concentration, compared with wild type, under the following conditions ... 

Antibiotics, additives carbenicillin, isopropyl-/3-D-thiogalactoside (IPTG)... 

Induce with isopropyl- S-D-thiogalactoside (IPTG solution) 10 pL of a sterile filtered solution (100 mg mL-1) in pure ethanol. Incubate overnight at 37 °C. 

APTG p-aminophenyl-/3-D-thiogalactoside IgG immunoglobulin G. Source Lottspeich, 1998. 

The activity of [i-galactosidasc (P-Gal) was studied on a quartz chip using a static micromixer to mix the enzyme and substrate on the ms time scale. Inhibition by phenylethyl-P-D-thio-galactoside was also studied [1048]. In another report, the enzyme P-Gal was assayed on a chip in which P-Gal would convert a substrate, resoruhn-P-D-galactopyranoside (RBG), to resoruhn to be detected fluorescently [1049]. By varying the substrate concentrations and monitoring the amount of resoruhn by LIF, Michaelis-Menten constants could be determined. In addition, the inhibition constants of phenylethyl-P-D-thiogalactoside, lactose, and p-hydroxymercuribenzoic acid to the enzyme P-Gal were determined [1049]. 

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