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VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
The volume of literature dealing with the metabolism of carbohydrate-type materials has grown enormously in recent years, to the point
that the authors have felt obliged to restrict the scope of this review
within more narrow limits. It has been decided to adhere to a fairly
literal interpretation of "saccharides" and to omit from this discussion
extensive mention of the metabolism of partial oxidation products of
saccharides, e.g., pyruvate. We will direct our attention to the metabolism (chiefly degradative) of saccharides per se, particularly of glucose and of a few of its close relatives. Partial oxidation products, when
they are discussed at all, will be mentioned from the standpoint of
saccharide metabolism, either as direct end products or as they may be
situated on the mainstream of terminal oxidation routes that supply
large amounts of energy from the oxidation of glucose.
In a previous volume, the traditional breakdown routes of carbohydrate metabolism, i.e., glycolysis and the Krebs citric acid cycle, have
been discussed.* In the minds of many biochemists, the central position
of these pathways is partly deserved, partly traditional. Other newer
metabolic routes which have been studied in detail in more recent years
have been shown, as will be described in these pages, to be of varying
significance on a comparative basis, and even (as the pentose cycle) to
be of as widespread occurrence as are the classic pathways referred to
above.
I. The Pentose Cycle
A. HISTORICAL INTRODUCTION
This route of carbohydrate breakdown, otherwise called the hexose
monophosphate "shunt," the "direct" oxidative pathway, the phosphogluconate oxidation scheme, or the pentose phosphate cycle, has been
recognized in toto since 1953, when Horecker described its operations
in considerable detail (I). Several stimulating reviews on the subject
have appeared (2, 2a, 2b, 2c, 3). Important fragments of this cycle,
however, have been recognized for nearly a quarter of a century, since
Warburg et al. (4), Lipmann (5), and Dickens (6) discovered that
glucose-6-phosphate could be oxidized to yield pentose without the
intervention of glycolysis.
Indeed, in retrospect, the reader may wonder why these principal
discoveries did not immediately trigger a more widespread search for
the details of this oxidative scheme; the citric acid cycle was actually
announced later (7) than the three papers cited in the foregoing para* See Vol. I, Chapter 9.
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
The volume of literature dealing with the metabolism of carbohydrate-type materials has grown enormously in recent years, to the point
that the authors have felt obliged to restrict the scope of this review
within more narrow limits. It has been decided to adhere to a fairly
literal interpretation of "saccharides" and to omit from this discussion
extensive mention of the metabolism of partial oxidation products of
saccharides, e.g., pyruvate. We will direct our attention to the metabolism (chiefly degradative) of saccharides per se, particularly of glucose and of a few of its close relatives. Partial oxidation products, when
they are discussed at all, will be mentioned from the standpoint of
saccharide metabolism, either as direct end products or as they may be
situated on the mainstream of terminal oxidation routes that supply
large amounts of energy from the oxidation of glucose.
In a previous volume, the traditional breakdown routes of carbohydrate metabolism, i.e., glycolysis and the Krebs citric acid cycle, have
been discussed.* In the minds of many biochemists, the central position
of these pathways is partly deserved, partly traditional. Other newer
metabolic routes which have been studied in detail in more recent years
have been shown, as will be described in these pages, to be of varying
significance on a comparative basis, and even (as the pentose cycle) to
be of as widespread occurrence as are the classic pathways referred to
above.
I. The Pentose Cycle
A. HISTORICAL INTRODUCTION
This route of carbohydrate breakdown, otherwise called the hexose
monophosphate "shunt," the "direct" oxidative pathway, the phosphogluconate oxidation scheme, or the pentose phosphate cycle, has been
recognized in toto since 1953, when Horecker described its operations
in considerable detail (I). Several stimulating reviews on the subject
have appeared (2, 2a, 2b, 2c, 3). Important fragments of this cycle,
however, have been recognized for nearly a quarter of a century, since
Warburg et al. (4), Lipmann (5), and Dickens (6) discovered that
glucose-6-phosphate could be oxidized to yield pentose without the
intervention of glycolysis.
Indeed, in retrospect, the reader may wonder why these principal
discoveries did not immediately trigger a more widespread search for
the details of this oxidative scheme; the citric acid cycle was actually
announced later (7) than the three papers cited in the foregoing para* See Vol. I, Chapter 9.