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.

Genetic evidence for the role of a bacterial phosphotransferase system in sugar transport.

Abstract: Enzyme II, the membrane-bound component of the system, determines its carbohydrate specificity; five such enzymes have thus far been identified. A close relationship between the phosphotransferase and carbohydrate permease systems was reported earlier4 based on results obtained with osmotically shocked Escherichia coli W2244;5 the cells lost most of their HPr along with their ability to transport two glycosides. Other transport systems were subsequently studied by this method.6-8 In the course of the present experiments, results obtained9, 10 with mutants of E. coli and Aerobacter aerogenes (lacking either enzyme I or HPr) showed that the phosphotransferase system was involved in either the transport and/or metabolism of five sugars. The present report is concerned with a single mutation in Salmonella typhimurium that results in an inability to grow on nine carbohydrates concomitant with a loss of enzyme I. The mutant was also seriously defective in its ability to transport sugars into the cell. We therefore conclude that the phosphotransferase system is intimately involved in sugar transport. Materials and Methods.-Unless otherwise specified, all materials were obtained from commercial sources. The parent strain, Salmonella typhimurium SB497 (rfb-816, his-1367), was grown in liquid culture in a mineral-salts medium, as described in Table 1, or in nutrient broth (Difco). To obtain the desired mutant, the parent strain was treated with nitrosoguanidine,"I grown in the mineral medium in the presence of melibiose and penicillin,12 and the resulting culture spread on eosiin-methylene blue plates (EMB) containing melibiose in order to obtain melibiose-negative colonies. Several such colonies were only melibiose-negative, while one mutant, designated SB703, lacked the ability to ferment eight other carbohydrates, as described below. This carbohydrate lesion was termed car-, by analogy with the carmutants of Staphylococcus aureus."3 Fermentation tests were conducted on peptone EMB plates,'4 or on the more sensitive bromthymol blue indicator plates," in the presence of 1 per cent carbohydrate.

Disruption of regulatory gene GAL80 in Saccharomyces cerevisiae: effects on carbon-controlled regulation of the galactose/melibiose pathway genes.

Abstract: In Saccharomyces cerevisiae, the transcriptional expression of the galactose-melibiose catabolic pathway genes is under the control of at least three regulatory genes, GAL4, GAL80, and GAL3. We have isolated the GAL80 gene and have studied the effect of a null mutation on the carbon-controlled regulation of the MEL1 and GAL cluster genes. The null mutation was achieved in vivo by replacing the chromosomal wild-type GAL80 allele with an in vitro-created GAL80 deletion-disruption mutation. Enzyme activities and RNA levels for the GAL cluster and MEL1 genes were constitutively expressed in the null mutant strain grown on glycerol-lactate and were higher than in the isogenic wild-type yeast strain when compared after growth on galactose. Carbon catabolite repression of the GAL cluster and MEL1 genes, which occurs at the level of transcription, is retained in the null mutant. Deletion of the GAL80 gene in a gal4 cell does not restore GAL cluster and MEL1 gene expression. The data demonstrate that (i) the GAL80 protein is a purely negative regulator, (ii) the GAL80 protein does not mediate carbon catabolite repression, and (iii) the GAL4 protein is not simply an antagonizer of GAL80-mediated repression.

β-Galactosidase of Streptococcus lactis

Abstract: Citti, J. E. (Oregon State University, Corvallis), W. E. Sandine, and P. R. Elliker. β-Galactosidase of Streptococcus lactis. J. Bacteriol. 89:937–942. 1965.—Synthesis of β-galactosidase by several strains of Streptococcus lactis was induced by lactose. The rate of hydrolysis of o-nitrophenyl-β-d-galactopyranoside was used to measure enzyme activity. The enzyme of all but one strain was unstable when whole cells were sonic-treated or treated with toluene; the enzyme of one strain of S. lactis was stable to these treatments, which resulted in at least a fivefold increase in activity over that found in whole cells. The optimal assay conditions for toluene-treated cells of this strain involved incubation at 37 C in pH 7.0 sodium phosphate buffer. Lactose was the most effective inducer of enzyme synthesis. Methyl-β-d-thiogalactopyranoside, isopropyl-β-d-thiogalactopyranoside, and galactose were also inducers of the enzyme, but were not as effective as lactose. Melibiose, maltose, and calcium lactobionate were poor inducers of enzyme synthesis. Exogenously supplied glucose repressed enzyme synthesis. The means of control of induced β-galactosidase synthesis in S. lactis was similar to that in Escherichia coli.

Role of Na+ and Li+ in thiomethylgalactoside transport by the melibiose transport system of Escherichia coli.

Abstract: Thiomethyl-beta-galactoside (TMG) accumulation via the melibiose transport system was studied in lactose transport-negative strains of Escherichia coli. TMG uptake by either intact cells or membrane vesicles was markedly stimulated by Na+ or Li+ between pH 5.5 and 8. The Km for uptake of TMG was approximately 0.2 mM at an external Na+ concentration of 5 mM (pH 7). The alpha-galactosides, melibiose, methyl-alpha-galactoside, and o-nitrophenyl-alpha-galactoside had a high affinity for this system whereas lactose, maltose and glucose had none. Evidence is presented for Li+-TMG or Na+-TMG cotransport.