ISSN:
0749-503X
Keywords:
Fluorocytosine
;
energy dissipation
;
cytosine permease
;
Saccharomyces cerevisiae
;
Life and Medical Sciences
;
Genetics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
At-pH 5-6 ATP-depleted washed cell preparations of strain NC233-10b[pII4-9], in which the cytosine permease was overexpressed, absorbed cytosine, hypoxanthine or fluorocytosine stoichiometrically with, respectively, about 1, 1·4 and 5 proton equivalents. The cellular pH fell proportionately. The membrane depolarization caused by each compound was assayed in the presence of glucose with a voltage-sensitive dye and increased in the same order. Fluorocytosine significantly lowered the growth yield that a ‘petite’ strain of the yeast formed at limiting glucose concentrations. At pH 5·6 with extracellular [K+] below 1 mM, each of the three substrates was accumulated about 200-fold from a dilute solution at the expense of the proton gradient. This concentration ratio corresponds to a solute gradient (Δμs) of 13 kJ mol-1. Raising [K+]0 systematically lowered the substrate accumulation ratio and ΔμH. The mean ratio Δμs/ΔμH was 0·82 all three substrates. It was concluded that whereas the behaviour of cytosine approximated to that expected for a symport of unit proton stoichiometry, the absorption of protons with fluorocytosine and, to a lesser extent, hypoxanthine, was only partly conserved as useful work. A possible mechanism of this novel phenomenon is outlined.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/yea.320081208
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