464
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
ner similar to that of fruit glucose, i.e., mainly by way of glycolysis
(after initial formation of hexose phosphate), instead of engaging extensively in recycling. It is of interest to note that the operation of the
Entner-DoudorofiF pathway has not yet been demonstrated to be operative in plant tissues.
In microorganisms, including bacteria and fungi, catabolism of
glucose and its degradation products has been studied much more extensively than in either plants or animals. In fact, many of the metabolic
pathways were first recognized from findings using microorganisms as
test systems. This is perhaps not surprising in view of the fact that
microorganisms show characteristically vigorous metabolic rates. A
notable example was the work on the metabolism of glucose in the
pseudomonads which led to the discovery of the Entner-Doudoroff pathway for glucose degradation (114).
Examination of the existing literature prompts the suggestion that
several microorganisms may be classified (more so than previously has
been done) on the basis of their respective metabolic behaviors. Thus,
studies with pseudomonads, using the radiorespirometric technique,
have revealed that various species in this category are equipped to
catabolize glucose by way of the Entner-Doudoroff pathway either exclusively or combined with the pentose cycle (142). Similarly one finds
that in the related Acetobacter species examined (144, 154) the pentose
cycle plays a predominant or exclusive role in hexose metabolism.
Even more interesting is the fact that such organisms as bakers' yeast,
Escherichia colt, and B. subtilis show strong resemblance to each other
in the manner in which they attack carbohydrates. In each organism,
one can recognize easily the assimilation and depletion phases: during
assimilation while primary breakdown of glucose takes place, glycolysis
plays a preponderant role, with phosphogluconate cleavage occurring
to a limited extent. The predominance of the TCA cycle is revealed in
the depletion phase, C
14 0 2 being produced in the order C-2 > C-6
> C-l > C-3,4 from glucose.
Work done on the biosynthetic mechanisms for amino acids in microorganisms (198-200) has indicated the importance of the TCA cycle in
the production of carbon skeletons of numerous varieties. To maintain
the continuous operation of the TCA cycle, however, it is mandatory
that one or more of the key members of the cycle be furnished from an
independent mechanism. The elucidation of such mechanisms has attracted considerable interest from a number of research workers. Previously, the fixation of C0 2 in a C 3 -f- Ci or a C x + C 2 + C t condensation (both may take place via a number of possible mechanisms) have
been recognized as playing an important role (201-207). More recently
VERNON H. CHELDELIN, CHIH H. WANG, AND TSOO E. KING
ner similar to that of fruit glucose, i.e., mainly by way of glycolysis
(after initial formation of hexose phosphate), instead of engaging extensively in recycling. It is of interest to note that the operation of the
Entner-DoudorofiF pathway has not yet been demonstrated to be operative in plant tissues.
In microorganisms, including bacteria and fungi, catabolism of
glucose and its degradation products has been studied much more extensively than in either plants or animals. In fact, many of the metabolic
pathways were first recognized from findings using microorganisms as
test systems. This is perhaps not surprising in view of the fact that
microorganisms show characteristically vigorous metabolic rates. A
notable example was the work on the metabolism of glucose in the
pseudomonads which led to the discovery of the Entner-Doudoroff pathway for glucose degradation (114).
Examination of the existing literature prompts the suggestion that
several microorganisms may be classified (more so than previously has
been done) on the basis of their respective metabolic behaviors. Thus,
studies with pseudomonads, using the radiorespirometric technique,
have revealed that various species in this category are equipped to
catabolize glucose by way of the Entner-Doudoroff pathway either exclusively or combined with the pentose cycle (142). Similarly one finds
that in the related Acetobacter species examined (144, 154) the pentose
cycle plays a predominant or exclusive role in hexose metabolism.
Even more interesting is the fact that such organisms as bakers' yeast,
Escherichia colt, and B. subtilis show strong resemblance to each other
in the manner in which they attack carbohydrates. In each organism,
one can recognize easily the assimilation and depletion phases: during
assimilation while primary breakdown of glucose takes place, glycolysis
plays a preponderant role, with phosphogluconate cleavage occurring
to a limited extent. The predominance of the TCA cycle is revealed in
the depletion phase, C
14 0 2 being produced in the order C-2 > C-6
> C-l > C-3,4 from glucose.
Work done on the biosynthetic mechanisms for amino acids in microorganisms (198-200) has indicated the importance of the TCA cycle in
the production of carbon skeletons of numerous varieties. To maintain
the continuous operation of the TCA cycle, however, it is mandatory
that one or more of the key members of the cycle be furnished from an
independent mechanism. The elucidation of such mechanisms has attracted considerable interest from a number of research workers. Previously, the fixation of C0 2 in a C 3 -f- Ci or a C x + C 2 + C t condensation (both may take place via a number of possible mechanisms) have
been recognized as playing an important role (201-207). More recently