Transport of uridine in Escherichia coli B and A showdomycin-resistant mutant

Dippe, Patricia J. Von; Roy-Burman, S.; Visser, Donald W.

doi:10.1016/0005-2736(73)90340-4

Cited by 16 publications

(3 citation statements)

References 10 publications

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“…Similar observations on the specific re-tention of ribose-1-P and the exclusion of bases have been made for the uptake of several nucleosides by isolated mammalian plasma membrane vesicles incubated with several nucleosides (14,20,21). The present results also agree with a recent report (22) that ribose-1-P is selectively retained by intact E. coli B cells during uridine uptake.…”

Section: Discussionsupporting

confidence: 92%

Regulation of purine utilization in bacteria. VII. Involvement of membrane-associated nucleoside phosphorylase in the uptake and the base-mediated loss of the ribose moiety of nucleosides by Salmonella typhimurium membrane vesicles

Rader¹,

Hochstadt²

1976

J Bacteriol

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Although uridine and adenosine are converted by membrane-associated nuf cleoside phosphorylases to ribose-1-phosphate (ribose-1-P) and the corresponding bases (uracil and adenine), only ribose-1-P is accumulated within Salmonella typhimurium LT2 membrane vesicles. In accordance with these observations, no uptake is observed when the vesicles are incubated with the bases or nucleosides labeled in their base moieties. The vesicles lack a transport system for ribose-1-P, since excess ribose-1-P does not inhibit the uptake of the ribose moiety of uridine. In addition, there is no exchange with preaccumulated ribose-1-P. Thus, uridine, rather than ribose-1-P, must serve as the initially transported substrate. The uptake of the ribose portion of uridine is coupled to electron transport, and the levels to which ribose-1-P are accumulated may be reduced by adding various bases to the reaction mixtures. The bases appear to inhibit the uridine phosphorylase reaction and/or cause an efflux of ribose-1-P from the vesicles. This loss of ribose-1-P reflects the accumulation of nucleosides in the external medium after being synthesized within the membranes. Synthesis of the nucleosides from intravesicular ribose-1-P and exogenous bases proceeds even though the bases are not accumulated by the vesicles. Furthermore, ribose-1-P cannot significantly inhibit uridine phosphorylase activity unless the membranes are disrupted. These observations indicate that the membrane-associated nucleoside phosphorylases may have a transmembranal orientation with their base and ribose-1-P binding sites on opposite sides of the membranes. Such an asymmetric arrangement of these enzymes may facilitate the uptake of the ribosyl moiety ofnucleosides by a group translocation mechanism. Thus, nucleosides may be cleaved during the membrane transport process, with the resultant bases delivered to the external environment while ribose-1-P is shunted to the intravesicular space.

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Section: Discussionsupporting

confidence: 92%

Regulation of purine utilization in bacteria. VII. Involvement of membrane-associated nucleoside phosphorylase in the uptake and the base-mediated loss of the ribose moiety of nucleosides by Salmonella typhimurium membrane vesicles

Rader¹,

Hochstadt²

1976

J Bacteriol

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“…Scores of other careful reports arguing against a simple group translocation proposal have appeared. Von Dippe et al [15] remeasured K m for uracil uptake in E. coli and found a 100-times lower value than that reported earlier by Hochstadt [1]. Another report [13] established that there is a difference between the K m for transport and PRTase activity corresponding to a given base.…”

Section: Physiological Studiesmentioning

confidence: 89%

“…Another report [13] established that there is a difference between the K m for transport and PRTase activity corresponding to a given base. In a related organism E. coli B, Von Dippe et al [15] observed that uracil was concentrated 90-fold by energy-dependent active transport, suggesting that uracil-PRTase may not be necessary. Some authors have found that there is considerable dissimilarity between inhibitors of transport and PRTase activity [12,13,16].…”

Section: Physiological Studiesmentioning

confidence: 99%