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THE UPTAKE OF UREA BY CHLORELLA
Author(s) -
BEKHEET I. A.,
SYRETT P. J.
Publication year - 1979
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1979.tb07573.x
Subject(s) - urea , thiourea , dcmu , photosynthesis , chlorella , darkness , metabolism , chemistry , biochemistry , biophysics , nuclear chemistry , biology , algae , botany , organic chemistry , photosystem ii
S ummary The uptake of 14 C by urea‐grown cells of Chlorella (strain 211/8p) supplied with [ 14 C]urea was studied. Uptake was rapid in light with an apparent half‐saturation value ( K m ) for urea of 16·5 μM. Uptake was inhibited competitively by thiourea. Uptake of 14 C was inhibited by 6 × 10 −6 DCMU in light and was very much slower in darkness; nevertheless, under these conditions, rate of loss of 14 C from the medium was much the same as in illuminated non‐inhibited cultures. [ 14 C]urea was metabolized rapidly by the cells and, in illuminated cells after a 5 min exposure to [ 14 C]urea, less than 50 % of the soluble 14 C within the cells was in [ 14 C]urea. It is concluded that much of the measured 14 C uptake may have been due to conversion of [ 14 C]urea to 14 CO 2 followed by photosynthetic 14 CO 2 fixation. Nevertheless, when [ 14 C]urea in the cells was extracted and separated by thin‐layer chromatgraphy, there was clear evidence of accumulation at a concentration above that in the external medium and of light stimulation of uptake. It is suggested that, in view of the rapid metabolism of [ 14 C]urea by Chlorella , it may be preferable to study the uptake mechanism of this organism by using the urea analogue, thiourea.