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Journal of Bacteriology, January 2001, p. 461-467, Vol. 183, No. 2
Institute of Biological Science and
Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic
of China
Received 27 March 2000/Accepted 16 October 2000
Escherichia coli contains three biochemically distinct
fumarases which catalyze the interconversion of fumarate to
L-malate in the tricarboxylic acid cycle. Batch culture
studies indicated that fumarase activities varied according to carbon
substrate and cell doubling time. Growth rate control of fumarase
activities in the wild type and mutants was demonstrated in continuous
culture; FumA and FumC activities were induced four- to fivefold when
the cell growth rate (k) was lowered from 1.2/h to 0.24/h
at 1 and 21% O2, respectively. There was a twofold
induction of FumA and FumC activities when acetate was utilized instead
of glucose as the sole carbon source. However, these fumarase
activities were still shown to be under growth rate control. Thus, the
activity of the fumarases is regulated by the cell growth rate and
carbon source utilization independently. Further examination of FumA and FumC activities in a cya mutant suggested that growth
rate control of FumA and FumC activities is cyclic AMP dependent.
Although the total fumarase activity increased under aerobic
conditions, the individual fumarase activities varied under different
oxygen levels. While FumB activity was maximal during anaerobic growth (k = 0.6/h), FumA was the major enzyme under anaerobic
cell growth, and the maximum activity was achieved when oxygen was
elevated to 1 to 2%. Further increase in the oxygen level caused
inactivation of FumA and FumB activities by the high oxidized state,
but FumC activity increased simultaneously when the oxygen level was
higher than 4%. The same regulation of the activities of fumarases in response to different oxygen levels was also found in mutants. Therefore, synthesis of the three fumarase enzymes is controlled in a
hierarchical fashion depending on the environmental oxygen that the
cell encounters.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.2.461-467.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Oxygen- and Growth Rate-Dependent Regulation of
Escherichia coli Fumarase (FumA, FumB, and FumC)
Activity
*
Corresponding author. Mailing address: Institute of
Biological Science and Technology, National Chiao Tung University,
Hsinchu, Taiwan, Republic of China. Phone: 886-35-729289. Fax:
886-35-729288. E-mail: cpts{at}cc.nctu.edu.tw.
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