236
GEORGE G. LATIES
It is entirely possible that uncoupling agents, by increasing the rate of
electron transfer through the respiratory chain, and by essentially precluding the reversibility of oxidations within the respiratory chain, may
raise the DPN/DPNH ratio, and in that way stimulate glycolysis. However, experiments by Simon (1953a, c), French and Beevers (1953), and
Terner (1954) all offer examples of situations in which aerobic fermentation (hence increased glycolysis) is evoked at concentrations of the uncoupling agent which result in a rate of oxygen utilization equal to that
of the controls. Under such conditions it is unlikely that the DPN/DPNH
ratio has been displaced. In particular, Terner presents an experiment
in which p-nitrophenol increased the ζ>ο 2 > lowered the phosphate esterified, and raised the lactic acid produced compared to the control. Twice
the concentration of the uncoupling agent, while diminishing phosphorylation and increasing glycolysis to a still greater extent, failed to raise
the Qo 2 further. Therefore it may be deduced that the rate of aerobic
glycolysis depends primarily upon the level of phosphate acceptor, which
increases with increasing concentration of the uncoupling agent, and not
on the ratio of oxidized to reduced coenzyme, since that ratio, at the
same level of aerobic respiration, should remain the same.
At the concentration of dinitrophenol giving maximal respiratory stimulation, Beevers (1953) observed respiratory rates well in excess of the
control value (see Table 1) in corn coleoptiles, carrot root disks, corn
roots, and in sunflower epicotyls. Except in sunflower epicotyls, aerobic
fermentation was initiated in each case at concentrations of dinitrophenol
which produced a maximal oxygen uptake, and rose to a maximum, at
ten times the latter concentration, while the oxygen uptake declined. In
sunflower tissue maximal aerobic fermentation and maximal oxygen
utilization occurred at the same dinitrophenol concentration (see Newcomb, 1950).
Simon (1953c) has emphasized that the effect of uncoupling agents
may shift from a stimulatory effect upon respiration at certain concentrations, to inhibitory effects at higher concentrations. By noting the
parallelism of the effect of dinitrocresol concentration on the assimilation
of glucose in yeast to its evocation of aerobic fermentation, Simon concluded that the rise in aerobic fermentation in response to increasing dinitrocresol concentrations was owing to an increasing effectiveness of uncoupling, even though the respiration rate was simultaneously declining.
The same explanation may apply to the experiments of Beevers, in which
higher concentrations of the uncoupling agent are required for maximal aerobic fermentation than for maximal respiration. Beevers noted
an appreciable stimulation of the respiration in carrot root disks by a
given concentration of dinitrophenol before any aerobic fermentation
GEORGE G. LATIES
It is entirely possible that uncoupling agents, by increasing the rate of
electron transfer through the respiratory chain, and by essentially precluding the reversibility of oxidations within the respiratory chain, may
raise the DPN/DPNH ratio, and in that way stimulate glycolysis. However, experiments by Simon (1953a, c), French and Beevers (1953), and
Terner (1954) all offer examples of situations in which aerobic fermentation (hence increased glycolysis) is evoked at concentrations of the uncoupling agent which result in a rate of oxygen utilization equal to that
of the controls. Under such conditions it is unlikely that the DPN/DPNH
ratio has been displaced. In particular, Terner presents an experiment
in which p-nitrophenol increased the ζ>ο 2 > lowered the phosphate esterified, and raised the lactic acid produced compared to the control. Twice
the concentration of the uncoupling agent, while diminishing phosphorylation and increasing glycolysis to a still greater extent, failed to raise
the Qo 2 further. Therefore it may be deduced that the rate of aerobic
glycolysis depends primarily upon the level of phosphate acceptor, which
increases with increasing concentration of the uncoupling agent, and not
on the ratio of oxidized to reduced coenzyme, since that ratio, at the
same level of aerobic respiration, should remain the same.
At the concentration of dinitrophenol giving maximal respiratory stimulation, Beevers (1953) observed respiratory rates well in excess of the
control value (see Table 1) in corn coleoptiles, carrot root disks, corn
roots, and in sunflower epicotyls. Except in sunflower epicotyls, aerobic
fermentation was initiated in each case at concentrations of dinitrophenol
which produced a maximal oxygen uptake, and rose to a maximum, at
ten times the latter concentration, while the oxygen uptake declined. In
sunflower tissue maximal aerobic fermentation and maximal oxygen
utilization occurred at the same dinitrophenol concentration (see Newcomb, 1950).
Simon (1953c) has emphasized that the effect of uncoupling agents
may shift from a stimulatory effect upon respiration at certain concentrations, to inhibitory effects at higher concentrations. By noting the
parallelism of the effect of dinitrocresol concentration on the assimilation
of glucose in yeast to its evocation of aerobic fermentation, Simon concluded that the rise in aerobic fermentation in response to increasing dinitrocresol concentrations was owing to an increasing effectiveness of uncoupling, even though the respiration rate was simultaneously declining.
The same explanation may apply to the experiments of Beevers, in which
higher concentrations of the uncoupling agent are required for maximal aerobic fermentation than for maximal respiration. Beevers noted
an appreciable stimulation of the respiration in carrot root disks by a
given concentration of dinitrophenol before any aerobic fermentation