34
Ν. G. PON
cells, and if the lymphatic leukemic cells were compared with lymphocytes, the activity of G-6-P DH in the granulocytes of myeloid leukemia
was found to increase to three times that of normal granulocytes while
that of lymphatic leukemia decreased to one-third that of the normal
leukocytes.
Further evidence for the presence of transketolase and transaldolase
in rabbit polymorphonuclear leukocytes is derived from experiments
with labeled pentoses (252) and labeled hexoses (253). The incorporation of labeled bicarbonate was also investigated (254), but the percentage of incorporation was extremely low. Nevertheless, enough
labeled products were obtained for degradation, which showed a distribution pattern explainable only by a slow reversal of the 6-PG DH
reaction superimposed on a transaldolase exchange reaction.
Another type of regulation of the flow of glucose through the pentose
phosphate pathway occurs when human and guinea pig leukocytes are
allowed to metabolize the exogenous glucose in the presence of bicarbonate. In this case the respiration is completely insensitive to added
cyanide (255), whereas in phosphate medium respiration is inhibited
by this ion in the presence of glucose. A mechanism was proposed
involving the dicarboxylic acid shuttle and transhydrogenase or DPNoxidase to provide the necessary cofactors, TPN
+ and DPN
+ , for glucose
catabolism via glycolysis and the pentose phosphate cycle.
When foreign bodies are ingested by certain types of leukocytes,
for example, guinea pig neutrophilic granulocytes, glycolysis is stimulated (256). Furthermore, oxygen uptake and the preferential conversion
of glucose-l-C
14
to C
14 0 2 are increased (257). Since a TPN-linked
lactate dehydrogenase was found in these leukocytes, Evans and Karnovsky suggested that the following mechanism can account for the observations above (258): Phagocytosis yields a decrease in the intracellular pH
because of the increased lactate production due to a stimulated glycolysis. This lowered pH, in turn, activates both DPNH oxidase and the
TPN-linked lactate dehydrogenase since these enzymes have optimal
activities around pH 5. The regeneration of oxidized pyridine nucleotides
thus increases the rate of glycolysis as well as of the oxidative pentose
phosphate cycle.
Some final words should be said about ribonucleic acid pentose
metabolism. Lymphatic leukemic cells and Gardner lymphosarcoma cells
(as well as rat thymus, mouse spleen, rabbit appendix) were incubated
with variously labeled glucose, and the distribution pattern in the ribose
of the RNA-purine nucleotides was determined along with that in some
of the free amino acids (259). The results indicate that both the transketolase-transaldolase pathway and the direct oxidative pathway are of
Ν. G. PON
cells, and if the lymphatic leukemic cells were compared with lymphocytes, the activity of G-6-P DH in the granulocytes of myeloid leukemia
was found to increase to three times that of normal granulocytes while
that of lymphatic leukemia decreased to one-third that of the normal
leukocytes.
Further evidence for the presence of transketolase and transaldolase
in rabbit polymorphonuclear leukocytes is derived from experiments
with labeled pentoses (252) and labeled hexoses (253). The incorporation of labeled bicarbonate was also investigated (254), but the percentage of incorporation was extremely low. Nevertheless, enough
labeled products were obtained for degradation, which showed a distribution pattern explainable only by a slow reversal of the 6-PG DH
reaction superimposed on a transaldolase exchange reaction.
Another type of regulation of the flow of glucose through the pentose
phosphate pathway occurs when human and guinea pig leukocytes are
allowed to metabolize the exogenous glucose in the presence of bicarbonate. In this case the respiration is completely insensitive to added
cyanide (255), whereas in phosphate medium respiration is inhibited
by this ion in the presence of glucose. A mechanism was proposed
involving the dicarboxylic acid shuttle and transhydrogenase or DPNoxidase to provide the necessary cofactors, TPN
+ and DPN
+ , for glucose
catabolism via glycolysis and the pentose phosphate cycle.
When foreign bodies are ingested by certain types of leukocytes,
for example, guinea pig neutrophilic granulocytes, glycolysis is stimulated (256). Furthermore, oxygen uptake and the preferential conversion
of glucose-l-C
14
to C
14 0 2 are increased (257). Since a TPN-linked
lactate dehydrogenase was found in these leukocytes, Evans and Karnovsky suggested that the following mechanism can account for the observations above (258): Phagocytosis yields a decrease in the intracellular pH
because of the increased lactate production due to a stimulated glycolysis. This lowered pH, in turn, activates both DPNH oxidase and the
TPN-linked lactate dehydrogenase since these enzymes have optimal
activities around pH 5. The regeneration of oxidized pyridine nucleotides
thus increases the rate of glycolysis as well as of the oxidative pentose
phosphate cycle.
Some final words should be said about ribonucleic acid pentose
metabolism. Lymphatic leukemic cells and Gardner lymphosarcoma cells
(as well as rat thymus, mouse spleen, rabbit appendix) were incubated
with variously labeled glucose, and the distribution pattern in the ribose
of the RNA-purine nucleotides was determined along with that in some
of the free amino acids (259). The results indicate that both the transketolase-transaldolase pathway and the direct oxidative pathway are of