Energy conservation in the extreme thermophile Thermus thermophilus HB8 |
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Authors: | A McKay J Quilter C W Jones |
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Institution: | (1) Department of Biochemistry, University of Leicester, University Road, LE1 7RH Leicester, UK |
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Abstract: | Whole cells of the extreme thermophile Thermus thermophilus HB8 contained a membrane-bound respiratory chain (comprised of nicotinamide nucleotide transhydrogenase, NADH dehydrogenase, menaquinone, and cytochromes b, c, aa3, o), which exhibited a maximum H+/O quotient of approximately 8 g-ion H+·g-atom O-1 for the oxidation of endogenous substrates. Whole cell respiration at 70° at the expense of endogenous substrates or ascorbate-TMPD generated a transmembrane protonmotive force ( p) of up to 197 mV and an intracellular phosphorylation poteintial ( Gp), measured under similar conditions, of approximately 43.9 kJ·mol-1.The measured Gp/ p ratio thus indicated an H+/ATP quotient of approximately 2.3 g-ion H+·mole ATP-1. Glucose-limited continuous cultures of T. thermophilus at 60°, 70° and 78.5° exhibited extremely low moler growth yields (Y
O2
max
27.6 g cells·mol O
2
-1
; Y
glucose
max
64.4 g cells ·mol glucose-1) compared with mesophilic bacteria of similar respiratory chain composition and proton translocation efficiency. These low yields are probably at least partly explained by the extremely high permeability of the cytoplasmic membrane to H+, which thus causes the cells to respire rapidly in order to maintain the protonmotive force at a level commensurate with cell growth.Abbreviations TPMP+
triphenylmethylphosphonium cation
- FCCP
carbonylcyanide p-trifluoromethoxy phenythydrazone
- TMPD
N,N,N ,N -tetramethyl-p-phenylene diamine |
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Keywords: | Respiration Molar growth yields Thermophile Energy conservation |
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