Galactosidase in E. coli

Toxi-ChromoPad (EBPI, Ontario, Canada) is a simple method for evaluation of the toxicity of solid particles [25,26,32,39]. The test is based on the inhibition of the synthesis of (3-galactosidase in E. coli after exposure to pollutants. The method has been used to measure acute toxicity of sediment and soil and other solid samples. The test bacterial suspension is mixed with homogenized samples and incubated for 2 hours. A drop of the test solution is pipetted onto a fiberglass filter containing an adsorbed substrate. A color reaction indicates the synthesis of enzyme, while a colorless reaction indicates toxicity. It has previously been shown... 

Which of the follotving statements about (3-galactosidase in E. coli are correct ... 

Loomis, W.F., Jr., Magasanik, B. The relation of catabolite repression to the induction system for jS galactosidase in E. coli. J. molec. Biol. 

Thio- -D-galactopyranosides with either short aliphatic chains or short hydroxy-substituted chains on the sulphur atom are able to induce the synthesis of /S-D-galactosidase in E. coli cyanoalkyl, carbamoyl, methoxyalkyl, and epoxyalkyl l-thio-jS-D-galactopyranosides are also effective, whereas the sodium salts of thioalkyl l-thio-/S-D-galactopyranosides are able both to induce and to inhibit synthesis of the enzyme. The mechanism of transport of jS-D-galacto-sidase in membrane vesicles of E. coli has been discussed. ... 

Jacquet, M., Kepes, a. The step sensitive to catabolite repression and its reversal by 3 -5 cyclic AMP during induced synthesis of j5-galactosidase in E. coli. Biochem. biophys. Res. Commun. 36, 84—92 (I969). 

Husum et al. found that the hydrolytic activities of P-galactosidase from E. coli and the protease subtilisin in a 50 % aqueous solution of the water-miscible ionic liquid [BMIM][Bp4] were comparable to those in 50 % aqueous solutions of ethanol or acetonitrile (Entry 9) [37]. 

In order to account for the inability of many enzymes to bind the protonated form of the basic inhibitors or permanently cationic ones better than uncharged analogs (for example, yS-o-galactosidase from E. coli, and P-v>-glucosidase from almonds), it was proposed that the enzyme could proton-ate the inhibitor at the active site by a cationic acid (for example, protonated histidine). If proton transfer cannot occur, the attractive forces due to the carboxylate would be canceled by the repulsion from the cationic acid. Experimental evidence for this proposal is, however, still lacking. In fi-D-gn-lactosidase from E. coli, a tyrosine is presumed to be responsible for the protonation of substrates. ... 

The characterization of the nar promoter in E. coli with the intact nar operon on the chromosome was carried out. Expression of P-galactosidase was maximal when the nar promoter was induced at ODgoo =1-7 under anaerobic conditions in the presence of 1 % nitrate. At this optimal condition the induction ratio was approximately 250 and the specific P-galactosidase activity was approximately 7500 Miller units at ODgoo = 2.7 [35]. In this study, we used plasmid... 

Isolation of alkaline phosphatase from Escherichia coli in which 85% of the proline residues were replaced by 3,4-dehydro-proline affected the heat lability and ultraviolet spectrum of the protein but the important criteria of catalytic function such as the and were unaltered (12). Massive replacement of methionine by selenomethionine in the 0-galactosidase of E. coli also failed to influence the catalytic activity. Canavanine facilely replaced arginine in the alkaline phosphatase of this bacterium at least 13 and perhaps 20 to 22 arginyl residues were substituted. This replacement by canavanine caused subunit accumulation since the altered subunits did not dimerize to yield the active enzyme (21). Nevertheless, these workers stated "There was also formed, however, a significant amount of enzymatically active protein in which most arginine residues had been replaced by canavanine." An earlier study in which either 7-azatryptophan or tryptazan replaced tryptophan resulted in active protein comparable to the native enzyme (14). 

In the induction of enzymes of galactose metabolism in E. coli, three enzymes are involved -galactosidase (which catalyses the hydrolysis of the y -glycosidic bonds of lactose), galactose permease (which is responsible for transport of lactose across the cell membrane) and a third enzyme, A-protein, apparently not directly involved in galactose metabolism. The system has an environmental inducer, galactose, and in its presence the number of /)-galactosidase molecules rises from 5-10 to 10,000 within the cell. The addition of the inducer can increase the protein production in less than five minutes after its addition. Protein synthesis of these enzymes stops almost immediately in the absence of lactose. 

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