Factors accelerating pyrimidine production in <Emphasis Type="Italic">Deinococcus radiophilus</Emphasis> |
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Authors: | Don McPhail Man-Kim Cheung Judith Brown Margaret Shepherdson |
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Institution: | (1) School of Life Sciences, University of the West of England, Coldharbour Lane, Bristol, BS16 1QY, UK |
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Abstract: | In studying the pyrimidine synthesising pathway in Deinococcus radiophilus two instances of anomalous behaviour were observed. One was the strikingly different results obtained for two types of assay
for carbamoyl phosphate synthetase. Both depend on the fixation of 14C from the substrate bicarbonate to give radioactive products. In the coupled assay the carbamoyl phosphate product of the
enzyme is converted to carbamoyl aspartate in the presence of aspartate and aspartate transcarbamoylase. In the direct assay
aspartate is omitted from the reaction mixture and the carbamoyl phosphate is converted to urea. It was found that the radioactive
counts in the direct assay were about 5% of those measured in the coupled assay. The second anomaly was that omission of glutamine
from both assay mixtures had no significant effect on the fixation of radioactive carbon. These results suggested that aspartate
amino-N could be the source of nitrogen for glutamine synthesis by a substrate-channelled pathway which delivered glutamine
to carbamoyl phosphate synthetase, and that externally added glutamine could not access its binding site on the enzyme. |
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Keywords: | Molecular evolution Substrate-channelling Pyrimidine synthesis |
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