ISSN:
1617-4623
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. Uridine transport has been examined in wild type and mutant strains of Salmonella typhimurium. The nucleoside-specific system requires a functional uridine kinase (udk +) as well as a periplasmic binding protein. This transport system is specific for uridine and cytidine and does not appear to contribute significantly to the uptake of deoxythymidine nor the purine nucleosides. The transport of uridine is characterized by hyperbolic kinetics with an apparent K m for uridine of 4.3±0.4 μM. 2. Uracil is transported by a completely different system which requires a functional uracil phosphoribosyl transferase (upp +) and possesses a periplasmic binding protein. 3. Bacterial strains lacking uridine kinase (udk -) do not transport uridine, but do transport uracil. Conversely, strains lacking uracil phosphoribosyl transferase (upp -), transport uridine, but do not transport uracil. Thus, uridine is transported intact rather than cleaved to uracil plus the ribose moiety and subsequently transported. Furthermore, very little uridine phosphorylase (uridine+Pi→uracil+ribose-1-phosphate) is recovered in periplasmic shock fluids of S. typhimurium. 4. Periplasmic binding proteins were indentified for both uridine and uracil. Furthermore, the uridine binding protein is separate from uridine kinase. Thus, transport of uridine and uracil require the participation of a periplasmic binding protein and the appropriate “salvage” enzyme.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00267220
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