14 Glycolysis
14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.7.1
14.7.2
14.7.3
14.8
14.9
The Pathway from Hexose to Pyruvate
Glycogen Phosphorylases
Hexokinases
Phosphofructokinases
Aldolases
Glyceraldehyde Phosphate Dehydrogenases
Pyruvate Kinases
Pyruvate Kinase Isoenzymes of Mammals
Pyruvate Kinase Isoenzymes of Other Vertebrates
Pyruvate Kinases of Invertebrates
Further Glycolysis Enzymes
Gluconeogenesis
14.1 The Pathway from Hexose
to Pyruvate
The enzyme system of glycolysis (Fig. 14.1) is present in all animal cells. This pathway, together
with the citric acid cycle and respiratory chain
phosphorylation, is involved in the provision of
energy under aerobic conditions. In contrast to
other substrates, however, carbohydrates can also
serve as a source of energy under anaerobic
conditions. The reactions and end products of
anaerobic carbohydrate catabolism vary greatly
within the animal kingdom, and thus provide an
especially interesting subject for comparative biochemistry. However, glycolysis should be considered not only as a source of energy but also as the
starting point for the biosynthesis of important
structural components, e.g. hexose phosphate for
the biosynthesis of carbohydrates, dihydroxyacetone phosphate and glycerol phosphate for lipid
biosynthesis, and 3-phosphoglycerate and pyruvate for the biosynthesis of various amino acids.
The synthetic metabolism may constitute a considerable proportion of the total glycolytic turnover. Thus, in vertebrate liver and other lipogenic
tissues, the greater part of the pyruvate arising
from glycolysis and the subsequent acetyl-CoA is
used in fatty acid synthesis.
14.10 Anaerobiosis
14.10.1 Activity- and Habitat-Dependent Anaerobiosis
14.10.2 End Products of Anaerobic Metabolism
14.11 Pyruvate Reductases
14.11.1 Lactate Dehydrogenases of Vertebrates
14.11.2 Lactate Dehydrogenases of Invertebrates
14.11.3 Opine Dehydrogenases
14.12 Special Pathways of Anaerobic Energy Production
14.12.1 Synthesis of Ethanol and Acetic Acid
14.12.2 Synthesis of Succinate, Volatile Fatty Acids
and Alanine
References
The enzymes of glycolysis are a textbook
example of cytoplasmic localization. However,
they are not all found in soluble form in the cytosol; they may also be more or less tightly bound
to cytoplasmic structures such as membranes or
the cytoskeleton. The binding of enzymes to cell
structures has the effect of a metabolic compartmentalization and can change the kineticregulatory properties of the enzymes. This balance between free and bound enzymes is influenced by the concentration of low molecular
weight effectors. In vertebrate skeletal muscle,
triose phosphate isomerase binds to myofibrills
only when these already carry bound aldolase
or glyceraldehyde-3-phosphate dehydrogenase;
thus, the living muscle contains a mini-enzyme
complex which catalyses the reaction step from
fructose-1,6-bisphosphate to 3-phosphoglycerate
[234]. In glioma cells, glycolytic enzymes are
found to be associated with the inner side of the
plasma membrane [44]. The regulatory importance of the reversible binding of glycolytic enzymes to cell structures has often been postulated,
but this has also been contradicted [20, 193]. Very
convincing examples are found in the sea snails:
binding to structures in the muscles of Busycotypus canaliculatum is reduced during oxygen deficiency, and the rate of glycolysis diminishes; the
14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.7.1
14.7.2
14.7.3
14.8
14.9
The Pathway from Hexose to Pyruvate
Glycogen Phosphorylases
Hexokinases
Phosphofructokinases
Aldolases
Glyceraldehyde Phosphate Dehydrogenases
Pyruvate Kinases
Pyruvate Kinase Isoenzymes of Mammals
Pyruvate Kinase Isoenzymes of Other Vertebrates
Pyruvate Kinases of Invertebrates
Further Glycolysis Enzymes
Gluconeogenesis
14.1 The Pathway from Hexose
to Pyruvate
The enzyme system of glycolysis (Fig. 14.1) is present in all animal cells. This pathway, together
with the citric acid cycle and respiratory chain
phosphorylation, is involved in the provision of
energy under aerobic conditions. In contrast to
other substrates, however, carbohydrates can also
serve as a source of energy under anaerobic
conditions. The reactions and end products of
anaerobic carbohydrate catabolism vary greatly
within the animal kingdom, and thus provide an
especially interesting subject for comparative biochemistry. However, glycolysis should be considered not only as a source of energy but also as the
starting point for the biosynthesis of important
structural components, e.g. hexose phosphate for
the biosynthesis of carbohydrates, dihydroxyacetone phosphate and glycerol phosphate for lipid
biosynthesis, and 3-phosphoglycerate and pyruvate for the biosynthesis of various amino acids.
The synthetic metabolism may constitute a considerable proportion of the total glycolytic turnover. Thus, in vertebrate liver and other lipogenic
tissues, the greater part of the pyruvate arising
from glycolysis and the subsequent acetyl-CoA is
used in fatty acid synthesis.
14.10 Anaerobiosis
14.10.1 Activity- and Habitat-Dependent Anaerobiosis
14.10.2 End Products of Anaerobic Metabolism
14.11 Pyruvate Reductases
14.11.1 Lactate Dehydrogenases of Vertebrates
14.11.2 Lactate Dehydrogenases of Invertebrates
14.11.3 Opine Dehydrogenases
14.12 Special Pathways of Anaerobic Energy Production
14.12.1 Synthesis of Ethanol and Acetic Acid
14.12.2 Synthesis of Succinate, Volatile Fatty Acids
and Alanine
References
The enzymes of glycolysis are a textbook
example of cytoplasmic localization. However,
they are not all found in soluble form in the cytosol; they may also be more or less tightly bound
to cytoplasmic structures such as membranes or
the cytoskeleton. The binding of enzymes to cell
structures has the effect of a metabolic compartmentalization and can change the kineticregulatory properties of the enzymes. This balance between free and bound enzymes is influenced by the concentration of low molecular
weight effectors. In vertebrate skeletal muscle,
triose phosphate isomerase binds to myofibrills
only when these already carry bound aldolase
or glyceraldehyde-3-phosphate dehydrogenase;
thus, the living muscle contains a mini-enzyme
complex which catalyses the reaction step from
fructose-1,6-bisphosphate to 3-phosphoglycerate
[234]. In glioma cells, glycolytic enzymes are
found to be associated with the inner side of the
plasma membrane [44]. The regulatory importance of the reversible binding of glycolytic enzymes to cell structures has often been postulated,
but this has also been contradicted [20, 193]. Very
convincing examples are found in the sea snails:
binding to structures in the muscles of Busycotypus canaliculatum is reduced during oxygen deficiency, and the rate of glycolysis diminishes; the