56
Ν. G. PON
nucleosides (357). Both the mucosa and the muscularis of the stomach
were found to have the dehydrogenases of the pentose phosphate cycle
(353).
A number of tissues (liver, brain, heart, lung, kidney, adrenal glands,
and skeletal muscles) from the fetuses of human, rat, rabbit, and dog
can oxidize glucose to C0 2 , and, in many cases, with a preferential
release of the C-l of glucose (S62). The lowest C-6:C-l values were
observed for the fetal adrenal glands, and they were even lower in the
absence of oxygen. Th C-6:C-l of C0 2 , however, did not significantly
change in any of these tissues over a fetal development period from 8
to 25 weeks gestational age. The G-6-P DH activity, on the other hand,
is initially high in the guinea pig fetal liver but decreases with increasing
time of gestation (363). The placentas G-6-P DH and 6-PG DH, in rat,
rabbit, guinea pig, and human, also decrease slightly toward parturition.
When comparisons are made of rat liver G-6-P DH activity in the fetal
stage, newborn, and adult stage, the following numbers were obtained
(micromoles of TPN
+ reduced per minute per milligram of supernatant
protein) (364): 19-day fetus, 5.9; newborn, 8.8; 3-day, 7.3; 7-day, 5.6;
12-day, 4.3; 14-day, 2.8; and adult, 7.9. On a per microgram DNA phosphorus basis, essentially the same pattern was obtained. The specific
activity of the liver 6-PG DH also falls as the newborn rat ages (365).
A conflicting observation was made by Stave (366), who found that in
the liver and kidney of the fetal rabbit, just prior to birth, in newborns,
and in animals between 2 and 4 weeks old, there was no marked alteration of G-6-P DH activity relative to adult values. Human blood cells of
various types (leukocytes, thrombocytes, and erythrocytes) also give the
same decreasing pattern of G-6-P DH activity with aging of the cells
(367). The L-929 strain of mouse fibroblast cells, grown in tissue cultures, contain G-6-P DH, 6-PG DH, and pentose phosphate isomerase,
but not transketolase or transaldolase (368). Surprisingly, however,
ribose-5-phosphate is utilized by these cells although no sedoheptulose7-phosphate, glyceraldehyde-3-phosphate, or fructose-6-phosphate is
formed. Examination by cytochemical techniques showed that G-6-P DH
is present in both the intra- and the extramitochondrial regions (369).
Both G-6-P DH and 6-PG DH have been demonstrated in the tissuecultured Earl's L cells (370). Noteworthy are some studies on human
cell cultures in which skin biopsies were obtained from individuals with
normal levels of G-6-P DH in the erythrocytes as compared with an
individual with a deficiency of this enzyme (371). The cultured cells
displayed the same pattern; i.e., those from normal individuals gave
much higher G-6-P DH activity than that from the deficient individual.
Ν. G. PON
nucleosides (357). Both the mucosa and the muscularis of the stomach
were found to have the dehydrogenases of the pentose phosphate cycle
(353).
A number of tissues (liver, brain, heart, lung, kidney, adrenal glands,
and skeletal muscles) from the fetuses of human, rat, rabbit, and dog
can oxidize glucose to C0 2 , and, in many cases, with a preferential
release of the C-l of glucose (S62). The lowest C-6:C-l values were
observed for the fetal adrenal glands, and they were even lower in the
absence of oxygen. Th C-6:C-l of C0 2 , however, did not significantly
change in any of these tissues over a fetal development period from 8
to 25 weeks gestational age. The G-6-P DH activity, on the other hand,
is initially high in the guinea pig fetal liver but decreases with increasing
time of gestation (363). The placentas G-6-P DH and 6-PG DH, in rat,
rabbit, guinea pig, and human, also decrease slightly toward parturition.
When comparisons are made of rat liver G-6-P DH activity in the fetal
stage, newborn, and adult stage, the following numbers were obtained
(micromoles of TPN
+ reduced per minute per milligram of supernatant
protein) (364): 19-day fetus, 5.9; newborn, 8.8; 3-day, 7.3; 7-day, 5.6;
12-day, 4.3; 14-day, 2.8; and adult, 7.9. On a per microgram DNA phosphorus basis, essentially the same pattern was obtained. The specific
activity of the liver 6-PG DH also falls as the newborn rat ages (365).
A conflicting observation was made by Stave (366), who found that in
the liver and kidney of the fetal rabbit, just prior to birth, in newborns,
and in animals between 2 and 4 weeks old, there was no marked alteration of G-6-P DH activity relative to adult values. Human blood cells of
various types (leukocytes, thrombocytes, and erythrocytes) also give the
same decreasing pattern of G-6-P DH activity with aging of the cells
(367). The L-929 strain of mouse fibroblast cells, grown in tissue cultures, contain G-6-P DH, 6-PG DH, and pentose phosphate isomerase,
but not transketolase or transaldolase (368). Surprisingly, however,
ribose-5-phosphate is utilized by these cells although no sedoheptulose7-phosphate, glyceraldehyde-3-phosphate, or fructose-6-phosphate is
formed. Examination by cytochemical techniques showed that G-6-P DH
is present in both the intra- and the extramitochondrial regions (369).
Both G-6-P DH and 6-PG DH have been demonstrated in the tissuecultured Earl's L cells (370). Noteworthy are some studies on human
cell cultures in which skin biopsies were obtained from individuals with
normal levels of G-6-P DH in the erythrocytes as compared with an
individual with a deficiency of this enzyme (371). The cultured cells
displayed the same pattern; i.e., those from normal individuals gave
much higher G-6-P DH activity than that from the deficient individual.