ISSN:
0091-7419
Keywords:
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
After exposure to inosine, transport-competent plasma membrane vesicles isolated from SV -40-transformed Balb/c 3T3 cells accumulate intravesicular ribose 1-PO4 at a concentration 200-fold greater than the extravesicular concentration. An analysis of the purine nucleoside phosphorylase activity distribution in various subcellular fractions, relative to other enzyme activities, indicated the presence of plasma membrane-associated purine nucleoside phosphorylase activity. The plasma membrane vesicles appear relatively impermeable to hypoxanthine. However, hypoxanthine, which is a competitive inhibitor of the transport reaction, is the only compound tested capable of mediating efflux of already accumulated ribose 1-PO4. In addition, hypoxanthine does not result in the efflux of transported uridine which is accumulated in these membrane vesicles as uridine. Exogenous ribose 1-PO4 neither results in counterflow nor does it inhibit the original uptake reaction. The following transport reaction is proposed: uptake occurs by group translocation, mediated by membrane-localized purine nuceloside phosphorylase. The data are consistent with sites for inosine and hypoxanthine being on the outer membrane surface whereas the ribose 1-PO4 site is only on the inner surface.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400040402
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