Melibiose

About: Melibiose is a research topic. Over the lifetime, 1002 publications have been published within this topic receiving 27300 citations. The topic is also known as: Melibiose.

Occurrence and characterization of lympho-agglutinins in Indian plants.

Abstract: Lympho-agglutinins have been detected and characterized in 31 plant species. Out of these, 14 agglutinated only the neuraminidase-treated cells. The lectin-rich genera included Crotalaria and Erythrina (Fabaceae), Amaranthus (Amaranthaceae), Artocarpus (Moraceae) and Clerodendron (Verbenaceae). The new lectins varied in their potency and biological action spectra. The 3 Artocarpus species were found to be exceptionally potent and specific for melibiose, an alpha-D-galactoside. Among the most effective sugar inhibitors for other lectins were N-acetyl-galactosamine, lactose, galactose and asialofetuin/fetuin.

Mutagenesis of Acidic Residues in Putative Membrane-spanning Segments of the Melibiose Permease of Escherichia coli

Abstract: Individual substitution of Cys or Asn for Asp-31, Asp-51, Asp-55, or Asp-120, distributed in different membrane spanning segments of the NHz-terminal domain of melibiose (rnel) permease partially or completely inactivates Na’-linked sugar transport and stimulation of sugar binding on me1 permease by Na+ ions (Pourcher, T., Zani, M.-L., and Leblanc, G. (1993) J. Biol. Chem. 268, 3209-3215). To investigate further the effect of these substitutions on the cationic selectivity and coupling properties of me1 permease, H+-melibiose coupled transport, coupling between H’ and melibiose movements, sugar counterflow, and zero-trans sugar efflux by the mutant permeases were analyzed. The results provide additional evidence indicating that manipulation of some of these Asp in the membrane-spanning segments of me1 permease alters its cationic selectivity properties. The results also indicate that the individual mutations diversely affect me1 permease-coupling properties. For example, only permease with Asn in place of Asp-31 or Cys in place of Asp-51 retains the capacity to actively transport melibiose. On the other hand, replacing Asp-55 by Cys produces uncoupling of cosubstrate flows by the carrier but does not hamper sugar translocation. These and other features of the mutant permeases are used to discuss the relative participation of Asp-31, Asp-51, Asp-55, or Asp-120 to the me1 symport mechanism and to its ionic selectivity and also the existence of a possible gating mechanism that may contribute the obligatory coupling of cosubstrate flows by the symporter.

Control of H+/lactose coupling by ionic interactions in the lactose permease of escherichia coli

Abstract: A combinatorial approach was used to study putative interactions among six ionizable residues (Asp-240, Glu-269, Arg-302, Lys-319, His-322, and Glu-325) in the lactose permease. Neutral mutations were made involving five ion pairs that had not been previously studied. Double mutants, R302L/E325Q and D240N/H322Q, had moderate levels of downhill [14C]-lactose transport. Mutants in which only one of these six residues was left unchanged (pentuple mutants) were also made. A Pent269− mutant (in which only Glu-269 remains) catalyzed a moderate level of downhill lactose transport. Pent240− and Pent 322+ also showed low levels of downhill lactose transport. Additionally, a Pent240− mutant exhibited proton transport upon addition of melibiose, but not lactose. This striking result demonstrates that neutralization of up to five residues of the lactose permease does not abolish proton transport. A mutant with neutral replacements at six ionic residues (hextuple mutant) had low levels of downhill lactose transport, but no uphill accumulation or proton transport. Since none of the mutants in this study catalyzes active accumulation of lactose, this is consistent with other reports that have shown that each residue is essential for proper coupling. Nevertheless, none of the six ionizable residues is individually required for substrate-induced proton cotransport. These results suggest that the H+ binding domain may be elsewhere in the permease or that cation binding may involve a flexible network of charged residues.

Carbohydrase specificity in Saccharomyces hybrids.

Abstract: THE substrate specificity of the yeast carbohydrases has been studied by many authors1–3. It has been concluded4,5 that standard industrial yeasts—brewers', distillers' and bakers' yeasts—contain carbohydrases the substrate specificity of which is determined qualitatively only by the nature of the glucosidic terminal unit of the sugar substrate. On this basis, distinction has been made between the following: (1) a beta-fructofuranosidase which catalyses the removal by hydrolysis of the fructofuranosidic terminal from sucrose, raffinose, stachyose, gentianose and beta-methylfructofuranoside, (2) an alpha-glucosidase which catalyses the removal by hydrolysis of the alpha-glucosidic terminal from maltose, sucrose, turanose, melezitose and suitable synthetic alpha-alkyl glucosides and alpha-aryl glucosides, and (3) an alpha-galactosidase, which catalyses the hydrolyses of the alpha-galactosidic terminal from melibiose, raffinose and alpha-phenyl galactoside.

Production and properties of galactosidases from Corticium rolfsii.

Abstract: When Corticum rolfsii was grown in a medium containing bran extract under aerobic conditions, it secreted alpha-D-galactosidase and beta-D-galactosidase into the culture fluid. Pectin also stimulated the production of these enzymes, whereas galactose, glucose, and sucrose stimulated their production to a lesser degree. C. rolfsii produced greater amounts of both enzymes than Aspergillus niger. Both galactosidases in the culture medium hydrolyzed alpha- and beta-p-nitrophenyl-D-galactosides as well as lactose, stachyose, melibiose, and raffinose. Both exhibited optimal activity at pH 2 to 4 and were quite stable under acidic conditions. alpha-Galactosidase was separated from beta-galactosidase by column chromatography.