Linked Life Data

45782

Source:http://linkedlifedata.com/resource/pubmed/id/45782

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
1
pubmed:dateCreated
1994-8-30
pubmed:abstractText
The entry of Na+ or H+ into cells of Escherichia coli via the melibiose transport system was stimulated by the addition of certain galactosides. The principal cell used in these studies (W3133) was a lactose transport negative strain of E. coli possessing an inducible melibiose transport system. Such cells were grown in the presence of melibiose, washed, and incubated in the presence of 25 microM Na+. The addition of thiomethylgalactoside (TMG) resulted in a fall in Na+ concentration in the incubation medium. No TMG-stimulated Na+ movement was observed in uninduced cells. In an alpha-galactosidase negative derivative of W3133 (RA11) a sugar-stimulated Na+ uptake was observed in melibiose-induced cells on the addition of melibiose, thiodigalactoside, methyl-alpha-galactoside, methyl-beta-galactoside, and galactose, but not lactose. It was inferred from these studies that the substrates of the melibiose system enter the cell on the melibiose carrier associated with the simultaneous entry of Na+ when this cation is present in the incubation medium. Extracellular pH was measured in unbuffered suspensions of induced cells in order to study proton movement across the membrane of cells exposed to different galactosides. In the absence of external Na+ or Li+ the addition of melibiose or methyl-alpha-galactoside resulted in marked alkalinization of the external medium (consistent with H+-sugar cotransport). On the other hand TMG, thiodigalactoside, and methyl-beta-galactoside gave no proton movement under these conditions. When Na+ was present, the addition of TMG or melibiose resulted in acidification of the medium. This observation is consistent with the view that the entry of Na+ with TMG or melibiose carries into the cell a positive charge (Na+) which provides the driving force for the diffusion of protons out of the cell. It is concluded that the melibiose carrier recognition of cations differs with different substrates.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:issn
0149-046X
pubmed:author
pubmed:issnType
Print
pubmed:volume
2
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
63-79
pubmed:dateRevised
2000-12-18
pubmed:meshHeading
pubmed:year
1978
pubmed:articleTitle
Cation-sugar cotransport in the melibiose transport system of Escherichia coli.
pubmed:affiliation
Department of Physiology, Harvard Medical School, Boston, Massachusetts 02115.
pubmed:publicationType
Journal Article