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Results for “Thiogalactosides”

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At least 19 recordsLinked to original sources
PubMed1982

Kinetic analysis of H+/methyl beta-D-thiogalactoside symport in Saccharomyces fragilis.

A theoretical description of initial uptake kinetics of H+/sugar symport is given, with emphasis on the differences between carrier and non-carrier systems. Transport of methyl beta-D-thiogalactoside in Saccharomyces fragilis is shown to proceed via the inducible lactose transporter. Uptake of this sugar stimulates electrogenic H+ influx. Together with the correlation between methyl beta-D-thiogalactoside accumulation and the proton-motive force this shows that transport proceeds via H+ symport. Kinetic analysis of initial influx revealed that transport proceeds via a single transport system, sensitive to changes in membrane potential. The pH dependence of the kinetic parameters showed that Kapp is almost pH insensitive, whereas Vapp decreases strongly at increasing extracellular pH. It is shown that transport proceeds, most likely, via a non-carrier system, with random binding of H+ and sugar, in a system where binding of the first ligand does not influence binding of the second.

Biological Transport↗
PubMed1980

lac Thiogalactoside transacetylase of Escherichia coli K-12 and ML.

The lac thiogalactoside transacetylase was purified from both a wild-type Escherichia coli K-12 strain (H3000) and an E. coli ML strain (ML308). These enzymes are indistinguishable by using several criteria. The subunit molecular weight of the enzyme is 24,800, which is significantly less than the previously reported value of 30,000. Although the function of the thiogalactoside transacetylase is unknown, it is suggested that this enzyme plays an important role in lactose utilization since its structure and enzymatic activity have been conserved.

Acetyltransferases↗
PubMed1985

The amino acid sequence of thiogalactoside transacetylase of Escherichia coli.

The amino acid sequence of thiogalactoside transacetylase, a dimer, has been determined. The monomer contains 202 amino acid residues in a single polypeptide chain and has a molecular weight of 22,671. The analysis was carried out by treatment of the carboxymethylated protein with cyanogen bromide and with trypsin. All seven cyanogen bromide peptides were isolated in pure form and were ordered by peptides isolated from tryptic digests. The sequence analysis was aided by determination of the DNA sequence of the lacA gene. The amino terminus of the protein is heterogenous because the initiator methionine is only partially cleaved. Another rather unusual feature of this cytoplasmic protein is a very hydrophobic segment in the center portion of the chain. Comparison of the amino acid sequence of thiogalactoside transacetylase to those of the lac repressor, beta-galactosidase, and lactose permease did not reveal any marked similarities. Therefore, there is no obvious evolutionary relatedness among proteins of the Lactose Operon.

Acetyltransferases↗
PubMed1978

Na+-dependent methyl beta-thiogalactoside transport in Salmonella typhimurium.

We have studied the role of sodium ions in methyl beta-thiogalactoside (TMG) transport via the melibiose permease (TMG II) in Salmonella typhimurium. TMG uptake via TMG II in anaerobic, straved and metabolically poisoned cells is dependent on an inward-directed Na+ gradient. Cells which have been partially depleted of endogenous substrates show H+ extrusion upon sodium-stimulated TMG influx. Measurements of the electrochemical H+ gradient in cells, starved in different ways for endogenous substrates, suggest that this proton extrusion is probably not linked to the actual translocation mechanism but is the result of metabolism induced by TMG plug Na+ uptake.

Biological Transport↗
PubMed1984

Purification of thiogalactoside transacetylase by affinity chromatography.

Thiogalactoside transacetylase, the product of the lacA gene of the lactose operon of Escherichia coli, has been purified by an improved procedure. The enzyme binds tightly to immobilized Cibacron Blue F3GA columns and can be eluted by potassium chloride in high concentrations. Final purification was obtained by affinity chromatography on an agarose-coenzyme A column followed by gel filtration.

Acetyltransferases↗