ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Both Li+ and Na+ stimulated the uptake of thiomethylgalactoside by the melibiose transport system ofEscherichia coli. On the other hand, Li+ inhibited the growth of cells on melibiose as a sole source of carbon. This inhibition was specific for melibiose, and Li+ had no effect on growth of cells on glucose, galactose, lactose, or glycerol. The effect of the cation on melibiose transport was investigated in a mutant which cannot utilize glucose. After entry into this cell, melibiose is cleaved into glucose and galactose by α-galactosidase, and the resulting glucose is excreted. Since the entry step was found to be rate-limiting, glucose production could be taken as a measure of melibiose transport. Li+ inhibited the transport of melibiose, but not the induction of the melibiose operon nor the activity of α-galactosidase. Li+ was found to inhibit the entry ofp-nitrophenyl-α-d-galactoside, but notp-nitrophenyl-β-d-galactoside entry. Thus, the cation specificity for the melibiose membrane carrier varies with different transport substrates.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870393
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