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Regulation of ammonia assimilation in ammonia‐limited chemostat cultures of Escherichia coli ML 30: Evidence of bistability
Author(s) -
Müller P. J.,
von Frommannshausen Beate,
Schütz H.
Publication year - 1981
Publication title -
zeitschrift für allgemeine mikrobiologie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.58
H-Index - 54
eISSN - 1521-4028
pISSN - 0044-2208
DOI - 10.1002/jobm.19810210503
Subject(s) - chemostat , glutamine synthetase , glutamate dehydrogenase , bistability , ammonia , enzyme , dilution , biochemistry , escherichia coli , steady state (chemistry) , enzyme assay , chemistry , biophysics , biology , glutamine , amino acid , bacteria , thermodynamics , materials science , glutamate receptor , organic chemistry , physics , genetics , receptor , optoelectronics , gene
Abstract In a preceding paper evidence of two stationary stable states (bistability) in the specific activity of glutamine synthetase (GS) in ammonia‐limited steady‐state cultures of Escherichia coli ML 30 at dilution rates ( D ) about 0.15 h −1 was described (Müller et al. 1977). For better understanding of the regulation mechanisms leading to GS bistability chemostat experiments were performed over a wide range of dilution rates up to D = 0.8 h −1 . For each steady state the specific activities of GS and glutamate dehydrogenase (GDH) – the other key enzyme of the two NH 3 assimilation routes in E. coli – and in addition the remaining NH 3 concentration in the culture liquid were determined. Parallel to GS bistability two states of GDH activity and NH 3 concentration are found. The higher state of GS is connected with a lower GDH activity and NH 3 concentration. With rising D the GS activities decrease whereas GDH activities and NH 3 concentrations increase. Since no adenylation of the GS is detectable GS bistability seems to be regulated on the level of enzyme synthesis like GDH bistability. From the experimental findings a mathematical model is derived based on the bottle neck enzyme theory of growth. It describes the dependence between the specific growth rates on the one hand and the specific enzyme activities and NH 3 concentration on the other. It is shown that the specific uptake rate of the limiting NH 3 and the specific growth rates, respectively, depend on the simultaneous action of two bottle neck enzymes which are connected by a regulative link.