1. PENTOSE PHOSPHATE CYCLE
65
variously labeled glucose are consistent with the predominant operation
of the EMP pathway in this organism.
Other organisms of this phylum exhibiting G-6-P DH activity are the
ameba Chaos chaos (419) and the parasitic flagellate Trypanosoma rhodesiense (420). The latter has been cultivated in an artificial medium
and in the bloodstream; both forms have this dehydrogenase which is
only TPN
+ specific. In the homogenate of the cultured form, the G-6-P
DH activity in the particulate fraction is twice that of the soluble supernatant fraction. No 6-PG DH was found in homogenates of either form.
A search was made for Entner-Doudoroff enzymes in either Trypanosoma cruzi or in T. rhodesiense, but with no success.
XIV. Bacteria and Fungi
Because the pathways of metabolism of glucose in these microorganisms have been elegantly reviewed by Cheldelin et al. (421), this reviewer has decided not to cover these two divisions of the plant kingdom. Their treatment of the subject is not only on a semiquantitative
basis, but is extensive enough to have represented most of the important
organisms of the microbial world. Admittedly, a given species of a particular genus does not necessarily utilize the same pathway for glucose
metabolism as another species. For example, radiorespirometry showed
that glucose metabolism in the genus Arthrobacter is of two types:
type 1, which relies heavily on the operation of the EMP pathway with
perhaps a minor contribution of the pentose phosphate cycle; and type 2,
which involves mainly the Entner-Doudoroff scheme and the pentose
phosphate cycle with glucose passing through gluconate (422). Bacteria
possessing the first type of metabolism are A. ureafaciens and A. globiformis, and those having the second type are A. simplex and A. atrocyaneus. The other problem facing the reader is that any review article,
no matter how new, cites references at least one or two years old, thus
recent work would obviously be lacking. An example of a recent piece
of work is that of Eagon and Wang (423), on the species Pseudomonas
natriegens, which when grown in glucose aerobically, catabolizes glucose
primarily via the EMP pathway and to a minor extent by way of the
shunt.
One other important pathway that is barely mentioned in the review
article by Cheldelin et al. is the reductive pentose phosphate cycle. This
cycle, initially believed to be associated only with photosynthetic organisms, was later demonstrated to be found also in nonphotosynthetic
organisms such as the bacteria. Fortunately, a review article dealing with
this topic has become available recently (424). Table XIII lists some of
the nonphotosynthetic microorganisms in which the reductive pentose
65
variously labeled glucose are consistent with the predominant operation
of the EMP pathway in this organism.
Other organisms of this phylum exhibiting G-6-P DH activity are the
ameba Chaos chaos (419) and the parasitic flagellate Trypanosoma rhodesiense (420). The latter has been cultivated in an artificial medium
and in the bloodstream; both forms have this dehydrogenase which is
only TPN
+ specific. In the homogenate of the cultured form, the G-6-P
DH activity in the particulate fraction is twice that of the soluble supernatant fraction. No 6-PG DH was found in homogenates of either form.
A search was made for Entner-Doudoroff enzymes in either Trypanosoma cruzi or in T. rhodesiense, but with no success.
XIV. Bacteria and Fungi
Because the pathways of metabolism of glucose in these microorganisms have been elegantly reviewed by Cheldelin et al. (421), this reviewer has decided not to cover these two divisions of the plant kingdom. Their treatment of the subject is not only on a semiquantitative
basis, but is extensive enough to have represented most of the important
organisms of the microbial world. Admittedly, a given species of a particular genus does not necessarily utilize the same pathway for glucose
metabolism as another species. For example, radiorespirometry showed
that glucose metabolism in the genus Arthrobacter is of two types:
type 1, which relies heavily on the operation of the EMP pathway with
perhaps a minor contribution of the pentose phosphate cycle; and type 2,
which involves mainly the Entner-Doudoroff scheme and the pentose
phosphate cycle with glucose passing through gluconate (422). Bacteria
possessing the first type of metabolism are A. ureafaciens and A. globiformis, and those having the second type are A. simplex and A. atrocyaneus. The other problem facing the reader is that any review article,
no matter how new, cites references at least one or two years old, thus
recent work would obviously be lacking. An example of a recent piece
of work is that of Eagon and Wang (423), on the species Pseudomonas
natriegens, which when grown in glucose aerobically, catabolizes glucose
primarily via the EMP pathway and to a minor extent by way of the
shunt.
One other important pathway that is barely mentioned in the review
article by Cheldelin et al. is the reductive pentose phosphate cycle. This
cycle, initially believed to be associated only with photosynthetic organisms, was later demonstrated to be found also in nonphotosynthetic
organisms such as the bacteria. Fortunately, a review article dealing with
this topic has become available recently (424). Table XIII lists some of
the nonphotosynthetic microorganisms in which the reductive pentose