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.

Proton-linked sugar transport systems in bacteria.

Abstract: The cell membranes of various bacteria contain proton-linked transport systems for D-xylose, L-arabinose, D-galactose, D-glucose, L-rhamnose, L-fucose, lactose, and melibiose. The melibiose transporter of E. coli is linked to both Na+ and H+ translocation. The substrate and inhibitor specificities of the monosaccharide transporters are described. By locating, cloning, and sequencing the genes encoding the sugar/H+ transporters in E. coli, the primary sequences of the transport proteins have been deduced. Those for xylose/H+, arabinose/H+, and galactose/H+ transport are homologous to each other. Furthermore, they are just as similar to the primary sequences of the following: glucose transport proteins found in a Cyanobacterium, yeast, alga, rat, mouse, and man; proteins for transport of galactose, lactose, or maltose in species of yeast; and to a developmentally regulated protein of Leishmania for which a function is not yet established. Some of these proteins catalyze facilitated diffusion of the sugar without cation transport. From the alignments of the homologous amino acid sequences, predictions of common structural features can be made: there are likely to be twelve membrane-spanning alpha-helices, possibly in two groups of six; there is a central hydrophilic region, probably comprised largely of alpha-helix; the highly conserved amino acid residues (40-50 out of 472-522 total) form discrete patterns or motifs throughout the proteins that are presumably critical for substrate recognition and the molecular mechanism of transport. Some of these features are found also in other transport proteins for citrate, tetracycline, lactose, or melibiose, the primary sequences of which are not similar to each other or to the homologous series of transporters. The glucose/Na+ transporter of rabbit and man is different in primary sequence to all the other sugar transporters characterized, but it is homologous to the proline/Na+ transporter of E. coli, and there is evidence for its structural similarity to glucose/H+ transporters in Plants. In vivo and in vitro mutagenesis of the lactose/H+ and melibiose/Na+ (H+) transporters of E. coli has identified individual amino acid residues alterations of which affect sugar and/or cation recognition and parameters of transport. Most of the bacterial transport proteins have been identified and the lactose/H+ transporter has been purified. The directions of future investigations are discussed.

The handling of soya alpha-galactosides by a normal and a galactosemic child.

Abstract: 1. No alpha-galactosidase activity in homogenates of human small intestinal mucosa was demonstrated either with stachyose, raffinose, or melibiose. 2. In a healthy child, oral raffinose and melibiose loads failed to produce changes in blood glucose, blood galactose, or red cell galactose-1-phosphate. Trace amounts of either saccharide were excreted in the urine. Following the raffinose load, diarrhea occurred and raffinose and melibiose as well as their hydrolysis products were found in the feces. 3. In a galactosemic patient, red cell galactose-1-phosphate rose as expected after ingestion of 2 gm of galactose. No such rise was seen after administration of equivalent and of double equivalent amounts of stachyose. Prolonged dietary supplementation with raffinose did not significantly alter non-fasting erythrocyte galactose-1-phosphate. 4. It is concluded that soybean formulas are generally safe for galactosemic infants; however, caution is advised for patients suffering from diarrhea.

Isolation and preliminary characterization of the GAL4 gene, a positive regulator of transcription in yeast

Abstract: The GAL4 locus encodes a positive regulator of the inducible galactose and melibiose genes of yeast. Using the yeast plasmid vector YEp13, we have cloned GAL4 by complementation of a gal4 mutation. Restriction endonuclease mapping of subclone DNA has delimited the region sufficient for complementation to a 3.2-kilobase segment of DNA. The GAL4 mRNA is 2.8 kilobases long, sufficient to encode a protein as large as 105,000 daltons. The concentration of the GAL4 transcript is about 0.1 per cell and is almost identical in galactose-induced and noninduced cells. This result is consistent with a previously proposed model in which the activity of the GAL4 protein and not the transcription of the GAL4 gene is modulated by galactose induction.

Sugars and Organic Acids of Vitis vinifera.

Abstract: Glucose, fructose, galactose, sucrose, maltose, melibiose, raffinose, and stachyose were identified in the leaves, bark, roots, and berries of Vitis vinifera L. var. Thompson Seedless. In addition to these sugars, verbascose and manninotriose were found in the leaves and bark. Malic, tartaric, citric, isocitric, ascorbic, cis -aconitic, oxalic, glycolic, glyoxylic, succinic, lactic, glutaric, fumaric, pyrrolidone carboxylic, α-ketoglutaric, pyruvic, oxaloacetic, galacturonic, glucuronic, shikimic, quinic, chlorogenic, and caffeic acids were identified in the leaves, bark, roots, and berries. Glucose, fructose, sucrose, malate, tartrate, and citrate were determined quantitatively in the leaf, petiole, xylem, bark, tendril, bud, puduncle pedicel, berry, lateral roots, and main roots at 4 separate physiological stages of growth. In addition, changes in the concentrations of fructose, glucose, malate, and tartrate in leaves were measured during a 36-day period starting from budburst.