Oxidative phosphorylation in intact Azotobacter vinelandii

Oxidative phosphorylation in intact chl-r mutants of Escherichia coli K 12

The efficiency of oxidative phosphorylation was estimated in intact resting cells of Escherichia coli K 12, strain PA 601 (chl-s) and its chl-r mutants, all of them grown anaerobically in the presence of nitrate. The oxidation of endogenous NADH in intact chl-s cells was accompanied by the formation of ATP whatever the terminal electron acceptor, oxygen or nitrate, so that it was possible to conclude that the energy conservation sites are operating with either of the two acceptors in cells grown anaerobically in the presence of nitrate. For chl-r mutants oxidation of endogenous NADH correlated with ATP-production was found only with oxygen as electron acceptor. It is concluded that the energy-conservation sites are preserved in these mutants, the nitrate respiratory chain of which is altered. This assumption is corroborated by the effects of uncouplers of oxidative phosphorylation on ATP-synthesis.

The energetics of Escherichia coli during aerobic growth in continuous culture

1. The energetics of Escherichia coli W growing aerobically in continuous culture have been investigated. Conditions were chosen such that growth was limited by the availability of carbon or oxygen (energy-limited cultures), or of ammonium of sulphate ions (excess energy cultures). 2. Under glycerol-limited conditions YmaxO2 (true molar growth yield with respect to oxygen) and YmaxATP (true molar growth yield with respect to ATP equivalents) were 50.9 g cells-mol O-02(-1) and 12.7 g cells-mol ATP equivalents-1 respectively; these values were not substantially altered during growth limited by oxygen, ammonium or sulphate. In contrast, M (the energy requirement for maintenance purposes) increased from approximately 2 mmol ATP equivalents-h-1-g cells-1 during energy-limited growth to 16.8 and 30.8 mmole ATP equivalents-h-1-g cells-1 when growth was limited by ammonium and sulphate ions respectively. 3. Replacement of glycerol by other limiting carbon sources caused YmaxATP to alter within the range 13.9 (glucose) to 7.1 (acetate) g cells-mol ATP equivalents-1 in the order glucose greater than galactose greather than arabinose greater than fructose greater than glycerol greater than fumarate greater than lactate greater than pyruvate greater than acetate. In each case the experimental value of YmaxATP was less than or equal to 55% of the theoretical value calculated from the known energy requirements for the biosynthesis of cell materials. 4. It is concluded from these results that neither M nor Ymax ATP are constant values for E. coli. M varies with the energy supply, being highest under excess energy growth conditions where it may reflect energy wastage by the cell. On the other hand, YmaxATP varies with the nature of the growth substrate and thus reflects the different energy requirements for the synthesis of cell material from different carbon sources.

Energy metabolism of Bdellovibrio bacteriovorus. II. P/O ratio and ATP pool turnover rate

The P/O ratio of Bdellovibrio bacteriovorus, strain Bd 109 Sa, was evaluated by two different methods based on the determination of energy-rich phosphate bonds and either NADH oxidation or oxygen-uptake. P/O values calculated on the basis of NADH oxidation were up to 6, which has to be regarded as being overestimated. P/O values calculated from energy-rich phosphate bonds and oxygen uptake were around 2. The P/O values determined for Escherichia coli B were similar. The loss of phosphorylation efficiency at one site is discussed. The ATP pool turnover rate of Bdellovibrio was 8/min during endogenous respiration and 24/min during substrate respiration. The corresponding values in Escherichia coli B were 3/min and 38/min.

Effects of varying the carbon source limiting growth on yield and maintenance characteristics of Escherichia coli in continuous culture

The magnitudes of Yo (grams [dry weight] formed per gram of atom O) and mo, the maintenance respiration (milligram-atoms of O per gram [dry weight] per hour), of Escherichia coli B have been determined by growing the organism in aerobic continuous culture limited by a number of different substrates. The value found were as follows: glucose--tyo = 12.5, mo = 0.9; glucose plus 2.7 mM cyclic adenosine 3',5'-monophosphate (cAMP)--Yo = 31.2, mo = 9.3; galactose--Yo = 13.2, mo = 1.8; mannitol--Yo = 20.1, mo = 6.1; L-glutamate--Yo = 25.5, mo = 17.7; glycerol--Yo = 14.9, mo = 10.0; succinate--Yo = 11.2, mo = 12.1; and acetate--Yo = 14.7, mo = 25.4. During growth in anaerobic continuous culture with limiting glucose YATP was found to be 10.3 g (dry weight)/mol of adenosine 5'-triphosphate (ATP) and m ATP was 18.9 mmol of ATP/g (dry weight) per h. The aerobic growth yields of cells growing on glucose, glucose plus cAMP, mannitol, and glutamate were consistent with the hypothesis that carbohydrates partially repress oxidative phosphorylation, but the yields of cells growing on glycerol, succinate, acetate, and galactose were all lower than expected. We conclude that, like the efficiency of oxidative phosphorylation, both the maintenance respiration and the amount of ATP necessary to serve maintenance processes are determined by the identity of the growth substrates. Yields smaller than expected may be explained by the absence of respiratory control exerted by phosphate acceptors.