424
ERNEST BUEDING AND EMMANUEL FÄRBER
during triosephosphate oxidation, is not reoxidized by means of the reduction of pyruvate to lactate catalyzed by lactic dehydrogenase; this
reoxidation is brought about by the reduction of dihydroxyacetone
phosphate to glycerophosphate. Glycerophosphate in turn is rapidly oxidized to dihydroxyacetone phosphate by a non-pyridine-linked dehydrogenase present in the sarcosomes (mitochondria). The electron transfer
from glycerophosphate to oxygen occurs through the cytochrome system
with the generation of ATP with a P: O ratio approaching 2 (200). The
sarcosomal oxidation of glycerophosphate is at least 10 times as active
as the oxidation of any of the substrates of the Krebs tricarboxylic acid
cycle and apparently is sufficiently large to account for the very high
increase in oxygen uptake which occurs when the muscle passes from
the resting to the active state (189, 201).
F. VERTEBRATES
1. Normal Tissues
Glycolysis is of widespread occurrence in the tissues of mammals and
of other vertebrates. Incubation of surviving preparations of virtually
every organ or tissue studied results in the formation of lactic acid from
added glucose or from endogenous glycogen (SO, 202-208). However,
the rate of glycolysis is very variable both under aerobic and anaerobic
conditions. Slices of some tissues, such as liver or kidney cortex, produce
relatively small amounts of lactic acid even anaerobically, whereas preparations of other cells, such as retina, jejunal mucosa, and kidney
medulla, are much more active both in the presence or absence of
oxygen. All tissues exhibit a marked Pasteur effect.
Poorly understood, however, is the importance of lactic acid production from glucose or glycogen in the economy of the cells of higher
animals. Since the majority of organs or tissues are unable to withstand
severe anoxia for more than minutes, it is obvious that anaerobic
glycolysis cannot sustain the life of such cells except in a few instances
(see below).
Aerobically, the evaluation of the possible importance of lactic acid
production from carbohydrate is complicated because the same EmbdenMeyerhof glycolytic scheme is used for the production of pyruvate, and
because of the occurrence in animal tissues of an alternate mechanism
for the initial breakdown of carbohydrate, i.e., the pentose phosphate
pathway (51, 64, 69). Pyruvate production via glycolysis is considered
to be of great importance in the preparation of hexoses and possibly
other sugars for the subsequent generation of most of the energy in the
carbohydrate molecule. However, even here, the quantitative importance
ERNEST BUEDING AND EMMANUEL FÄRBER
during triosephosphate oxidation, is not reoxidized by means of the reduction of pyruvate to lactate catalyzed by lactic dehydrogenase; this
reoxidation is brought about by the reduction of dihydroxyacetone
phosphate to glycerophosphate. Glycerophosphate in turn is rapidly oxidized to dihydroxyacetone phosphate by a non-pyridine-linked dehydrogenase present in the sarcosomes (mitochondria). The electron transfer
from glycerophosphate to oxygen occurs through the cytochrome system
with the generation of ATP with a P: O ratio approaching 2 (200). The
sarcosomal oxidation of glycerophosphate is at least 10 times as active
as the oxidation of any of the substrates of the Krebs tricarboxylic acid
cycle and apparently is sufficiently large to account for the very high
increase in oxygen uptake which occurs when the muscle passes from
the resting to the active state (189, 201).
F. VERTEBRATES
1. Normal Tissues
Glycolysis is of widespread occurrence in the tissues of mammals and
of other vertebrates. Incubation of surviving preparations of virtually
every organ or tissue studied results in the formation of lactic acid from
added glucose or from endogenous glycogen (SO, 202-208). However,
the rate of glycolysis is very variable both under aerobic and anaerobic
conditions. Slices of some tissues, such as liver or kidney cortex, produce
relatively small amounts of lactic acid even anaerobically, whereas preparations of other cells, such as retina, jejunal mucosa, and kidney
medulla, are much more active both in the presence or absence of
oxygen. All tissues exhibit a marked Pasteur effect.
Poorly understood, however, is the importance of lactic acid production from glucose or glycogen in the economy of the cells of higher
animals. Since the majority of organs or tissues are unable to withstand
severe anoxia for more than minutes, it is obvious that anaerobic
glycolysis cannot sustain the life of such cells except in a few instances
(see below).
Aerobically, the evaluation of the possible importance of lactic acid
production from carbohydrate is complicated because the same EmbdenMeyerhof glycolytic scheme is used for the production of pyruvate, and
because of the occurrence in animal tissues of an alternate mechanism
for the initial breakdown of carbohydrate, i.e., the pentose phosphate
pathway (51, 64, 69). Pyruvate production via glycolysis is considered
to be of great importance in the preparation of hexoses and possibly
other sugars for the subsequent generation of most of the energy in the
carbohydrate molecule. However, even here, the quantitative importance