Deviation from homeoviscous adaptation in Escherichia coli membranes.
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The process by which an organism changes the composition of its membranal fatty acids in response to growth temperature, so as to maintain optimal membrane functioning, is known as homeoviscous adaptation (HA). One expression of HA is the constancy of the fluorescence polarization (P) of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene (DPH) in membranes of cells grown at various temperatures. The P of DPH in the membranes of Escherichia coli was shown by us to be inversely proportional to bacterial growth rate on different carbon sources. This result, implying failure of HA, is now complemented by measurements of DPH lifetimes, which indicate that the dominant variables contributing to the drop in P are (a) the order parameter of the membrane, which goes down, and (b) the fluidity, which may slightly increase. These are then the changes induced by enhanced growth rate. Two additional effects, cell membrane permeability and sensitivity to thermal shock, determined by the diffusion of o-nitrophenylgalactoside (ONPG) and by exposure to 52 degrees C, respectively, are reported to increase with growth rate. We can now conclude that there is a deviation from the principle of HA in E. coli grown at various rates, brought about by controlling the growth media at constant temperatures. (+info)
Value of the O-nitrophenyl-beta-D-galactopyranoside test to differentiate among the aerobic actinomycetes.
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A comparative study to determine beta-D-galactosidase activity among 171 strains of aerobic actinomycetes (including mycobacteria and rhodococci) was performed by using two growth media and four O-nitrophenyl-beta-D-galactopyranoside (ONPG) substrates. The ONPG test was found to be a valuable screening test to differentiate between the ONPG-positive Nocardia spp. and the rapidly growing ONPG-negative mycobacteria and rhodococci. However, ONPG results varied significantly depending on the growth medium and test substrate used. (+info)
Transport of alpha-p-nitrophenylgalactoside by the lactose carrier of Escherichia coli.
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alpha-p-Nitrophenylgalactoside was found to be accumulated by the lactose transport-system of Escherichia coli. This fact may help to resolve the differences in the reported number of sugar binding sites of the lactose transport protein in nonenergized and energized membrane vesicles. (+info)
Opening the periplasmic cavity in lactose permease is the limiting step for sugar binding.
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Purification and characterization of two phospho-beta-galactosidases, LacG1 and LacG2, from Lactobacillus gasseri ATCC33323(T).
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Lactobacillus gasseri ATCC33323(T) expresses four enzymes showing phospho-beta-galactosidase activity (LacG1, LacG2, Pbg1 and Pbg2). We previously reported the purification and characterization of two phospho-beta-galactosidases (Pbg1 and Pbg2) from Lactobacillus gasseri JCM1031 cultured in lactose medium. Here we aimed to characterize LacG1 and LacG2, and classify the four enzymes into 'phospho-beta-galactosidase' or 'phospho-beta-glucosidase.' LacG1 and recombinant LacG2 (rLacG2), from Lb. gasseri ATCC33323(T), were purified to homogeneity using column chromatography. Kinetic experiments were performed using sugar substrates, o-nitrophenyl-beta-D-galactopyranoside 6-phosphate (ONPGal-6P) and o-nitrophenyl-beta-D-glucopyranoside 6-phosphate (ONPGlc-6P), synthesized in our laboratory. LacG1 and rLacG2 exhibited high k(cat)/K(m) values for ONPGal-6P as compared with Pbg1 and Pbg2. The V(max) values for ONPGal-6P were higher than phospho-beta-galactosidases previously purified and characterized from several lactic acid bacteria. A phylogenetic tree analysis showed that LacG1 and LacG2 belong to the phospho-beta-galactosidase cluster and Pbg1 and Pbg2 belong to the phospho-beta-glucosidase cluster. Our data suggest two phospho-beta-galactosidase, LacG1 and LacG2, are the primary enzymes for lactose utilization in Lb. gasseri ATCC33323(T). We propose a reclassification of Pbg1 and Pbg2 as phospho-beta-glucosidase. (+info)
Phage shock proteins B and C prevent lethal cytoplasmic membrane permeability in Yersinia enterocolitica.
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Purification and properties of beta-galactosidase from Aspergillus oryzae.
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Beta-Galactosidase [EC 3.2.1.23] has been purified from a culture of Aspergillus oryzae by 2-propanol fractionation, column chromatography on DEAE-Sephadex A-50 and Sephadex G-200. The preparation was homogeneous on ultracentrifugation and disc electrophoresis. The enzyme showed pH optima of 4.5 with ONPG-1 as a substrate and 4.8 with lactose as a substrate. The stable pH range was from 4.0 to 9.0 and the optimum temperature was 46 degrees. The Michaelis constants were 7.2 X 10-minus 4 M with ONPG and 1.8 X 10-minus 2 M with lactose. Hg-2+, Cu-2+, N-bromosuccinimide, and sodium laurylsulfate caused marked inhibition. The apparent molecular weight was calculated to be about 105,000 by Sephadex gel filtration and sucrose density gradient centrifugation. (+info)