414
ERNEST BUEDING AND EMMANUEL FÄRBER
extracts frequently is higher than in the intact cell. It appears that
glucose transport in certain mammalian tissues is subject to hormonal
control. For example, it has been shown that insulin increases glucose
transport into skeletal and heart muscles (7-16) while it has no effect
on this process in the red cell or in the brain (9, 10). Conversely, a
hormone of the anterior pituitary or a metabolic product thereof inhibits glucose transport (17). Glucose transport into red cells is inhibited also by phlorizin (18), and into schistosomes (19), as well as
into red cells (20), by alkyldibenzylamines.
B. ADP-ATP RATIOS
During glycolysis of glucose, twice as much ATP is produced than
is utilized (see ATP balance, Table I). Glycolysis cannot occur unless
ADP is supplied to serve as a phosphate acceptor from 1,3-diphosphoglycerate (Reaction 7) and from phosphoenolyruvate (Reaction 10).
The action of various ATPases which catalyze the irreversible hydrolysis
of ATP to ADP and inorganic phosphate represents one type of mechanism by which ADP is produced. The importance of ATPases in maintaining glycolysis has been demonstrated by Meyerhof and his associates (21, 22). For example, in yeast extracts hexosediphosphate accumulates because of the low ATPase activity of these preparations, resulting in a lack of phosphate acceptors (ADP). Addition of ATPase
brings about the formation of ADP which in turn produces a marked
stimulation of fermentation (23). This lack of ATPase explains why
glucose is fermented more rapidly by yeast extracts than is hexosediphosphate [Harden-Young effect (23)]: in contrast to the latter, fermentation of glucose or of fructose-6-phosphate results in the generation
of ADP. In the intact yeast cell ATPase activity must be considerably
greater than in cell-free extracts, because during the preparation of the
latter most of the ATPases are lost by destruction or adsorption on insoluble particles (24). A reverse picture prevails in homogenates of
brain, of tumor, and of embryonic tissues (24). In these preparations
ATPase activity is considerably higher than is hexokinase activity; therefore, a deficiency of ATP rather than of ADP prevails. Under these
conditions glycolysis is stimulated markedly by inhibitors of ATPases
(decyl alcohol, digitonin, sodium azide), by adsorption of ATPase on
cell particles removed by centrifugation (brain), or by the addition of
hexokinase (25-28). Another reaction which can affect the concentration
of ADP and of ATP is catalyzed by the enzyme creatine phosphokinase
(29).
Phosphocreatine + ADP <-> ATP + Creatine
ERNEST BUEDING AND EMMANUEL FÄRBER
extracts frequently is higher than in the intact cell. It appears that
glucose transport in certain mammalian tissues is subject to hormonal
control. For example, it has been shown that insulin increases glucose
transport into skeletal and heart muscles (7-16) while it has no effect
on this process in the red cell or in the brain (9, 10). Conversely, a
hormone of the anterior pituitary or a metabolic product thereof inhibits glucose transport (17). Glucose transport into red cells is inhibited also by phlorizin (18), and into schistosomes (19), as well as
into red cells (20), by alkyldibenzylamines.
B. ADP-ATP RATIOS
During glycolysis of glucose, twice as much ATP is produced than
is utilized (see ATP balance, Table I). Glycolysis cannot occur unless
ADP is supplied to serve as a phosphate acceptor from 1,3-diphosphoglycerate (Reaction 7) and from phosphoenolyruvate (Reaction 10).
The action of various ATPases which catalyze the irreversible hydrolysis
of ATP to ADP and inorganic phosphate represents one type of mechanism by which ADP is produced. The importance of ATPases in maintaining glycolysis has been demonstrated by Meyerhof and his associates (21, 22). For example, in yeast extracts hexosediphosphate accumulates because of the low ATPase activity of these preparations, resulting in a lack of phosphate acceptors (ADP). Addition of ATPase
brings about the formation of ADP which in turn produces a marked
stimulation of fermentation (23). This lack of ATPase explains why
glucose is fermented more rapidly by yeast extracts than is hexosediphosphate [Harden-Young effect (23)]: in contrast to the latter, fermentation of glucose or of fructose-6-phosphate results in the generation
of ADP. In the intact yeast cell ATPase activity must be considerably
greater than in cell-free extracts, because during the preparation of the
latter most of the ATPases are lost by destruction or adsorption on insoluble particles (24). A reverse picture prevails in homogenates of
brain, of tumor, and of embryonic tissues (24). In these preparations
ATPase activity is considerably higher than is hexokinase activity; therefore, a deficiency of ATP rather than of ADP prevails. Under these
conditions glycolysis is stimulated markedly by inhibitors of ATPases
(decyl alcohol, digitonin, sodium azide), by adsorption of ATPase on
cell particles removed by centrifugation (brain), or by the addition of
hexokinase (25-28). Another reaction which can affect the concentration
of ADP and of ATP is catalyzed by the enzyme creatine phosphokinase
(29).
Phosphocreatine + ADP <-> ATP + Creatine