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141.
Carbamoylphosphate synthetase (CPS) catalyzes the first committed step in
pyrimidine biosynthesis, arginine biosynthesis, or the urea cycle.
Organisms may contain either one generalized or two specific CPS enzymes,
and these enzymes may be heterodimeric (encoded by linked or unlinked
genes), monomeric, or part of a multifunctional protein. In order to help
elucidate the evolution of CPS, we have performed a comprehensive
phylogenetic analysis using the 21 available complete CPS sequences,
including a sequence from Sulfolobus solfataricus P2 which we report in
this paper. This is the first report of a complete CPS gene sequence from
an archaeon, and sequence analysis suggests that it encodes an enzyme
similar to heterodimeric CPSII. We confirm that internal similarity within
the synthetase domain of CPS is the result of an ancient gene duplication
that preceded the divergence of the Bacteria, Archaea, and Eukarya, and use
this internal duplication in phylogenetic tree construction to root the
tree of life. Our analysis indicates with high confidence that this
archaeal sequence is more closely related to those of Eukarya than to those
of Bacteria. In addition to this ancient duplication which created the
synthetase domain, our phylogenetic analysis reveals a complex history of
further gene duplications, fusions, and other events which have played an
integral part in the evolution of CPS.
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Volatilization of Mercury by Algae 总被引:1,自引:0,他引:1
The presence of Chlorella cells in a medium containing HgCl2 causes a rapid decrease of the mercury content in the algal suspension. The rate of decrease depends on the inoculum concentration. The presence of Hg in the medium induces a lag in the growth, whose length depends on the initial concentration of Hg and of the inoculum. Binding and/or uptake of mercury by the cells is not dependent on temperature. The mercury content per cell declines somewhat at the time at which the culture resumes growth at a rate similar to that of the controls without mercury. 相似文献
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MAYER L 《Biologie médicale》1951,40(3):200-204
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