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At least 1,063 records · Page 59Linked to original sources
PubMed1996

The lactose transporter in Leuconostoc lactis is a new member of the LacS subfamily of galactoside-pentose-hexuronide translocators.

The gene encoding the lactose transport protein (lacS) of Leuconostoc lactis NZ6009 has been cloned from its native lactose plasmid, pNZ63, by functional complementation of lactose permease-deficient Escherichia coli mutants. Nucleotide sequence analysis revealed an open reading frame with the capacity to encode a protein of 639 amino acids which had limited but significant identity to the lactose transport carriers (LacS) of Streptococcus thermophilus (34.5%) and Lactobacillus bulgaricus (35.6%). This similarity was present both in the amino-terminal hydrophobic carrier domain, which is homologous to the E. coli melibiose transporter, and in the carboxy-terminal enzyme IIA-like regulatory domain. The flanking regions of DNA surrounding lacS were also sequenced. Preceding the lacS gene was a small open reading frame in the same orientation encoding a deduced 95-amino-acid protein with a sequence similar to the amino-terminal portion of beta-galactosidase I from Bacillus stearothermophilus. The lacS gene was separated from the downstream beta-galactosidase genes (lacLM) by 2 kb of DNA containing an IS3-like insertion sequence, which is a novel arrangement for lac genes in comparison with that in other lactic acid bacteria. The lacS gene was cloned in an E. coli-Streptococcus shuttle vector and was expressed both in a lacS deletion derivative of S. thermophilus and in a pNZ63-cured strain, L. lactis NZ6091. The role of the LacS protein was confirmed by uptake assays in which substantial uptake of radiolabeled lactose or galactose was observed with L. lactis or S. thermophilus plasmids harboring an intact lacS gene. Furthermore, galactose uptake was observed in NZ6091, suggesting the presence of at least one more transport system for galactose in L. lactis.

Amino Acid Sequence↗
PubMed2004

Metabolic engineering of a phosphoketolase pathway for pentose catabolism in Saccharomyces cerevisiae.

Low ethanol yields on xylose hamper economically viable ethanol production from hemicellulose-rich plant material with Saccharomyces cerevisiae. A major obstacle is the limited capacity of yeast for anaerobic reoxidation of NADH. Net reoxidation of NADH could potentially be achieved by channeling carbon fluxes through a recombinant phosphoketolase pathway. By heterologous expression of phosphotransacetylase and acetaldehyde dehydrogenase in combination with the native phosphoketolase, we installed a functional phosphoketolase pathway in the xylose-fermenting Saccharomyces cerevisiae strain TMB3001c. Consequently the ethanol yield was increased by 25% because less of the by-product xylitol was formed. The flux through the recombinant phosphoketolase pathway was about 30% of the optimum flux that would be required to completely eliminate xylitol and glycerol accumulation. Further overexpression of phosphoketolase, however, increased acetate accumulation and reduced the fermentation rate. By combining the phosphoketolase pathway with the ald6 mutation, which reduced acetate formation, a strain with an ethanol yield 20% higher and a xylose fermentation rate 40% higher than those of its parent was engineered.

Aldehyde Oxidoreductases↗
PubMed1978

Pentose metabolism in Mycobacterium smegmatis: comparison of L-arabinose isomerases induced by L-arabinose and D-galactose.

D-Galactose, which did not serve as a growth substrate, was found to induce an L-arabinose isomerase of similar properties to the L-arabinose-induced L-arabinose isomerase. In both cases the pH profiles, pH stability, optimum temperature, heat stability, substrate specificity, metal ion requirements, mobility on polyacrylamide gel electrophoresis, and kinetic properties of the induced isomerases were identical. It appears possible that D-galactose was incorporated into the cells by an L-arabinose permease system that was alos induced by D-galactose.

Arabinose↗