Oxýt
hoá Phenylalanine, Leucine và Glucose trong mô Nhau Thai Người
In-Vitro Oxidation of Phenylalanine-1-14C,
Leucine-1-14C, and Glucose-1-14C-6-Phosphate in Human Placenta
Ngo Manh Tran, Marcel
Laplante et Etienne LeBel
Centre Hospitalier
Universitaire, Sherbrooke, Québec, Canada
Published in Journal of Nuclear Medicine, 12: 468-469,
1971.
An ionization chamber method was used for instantaneous and continuous measurement of 14CO2 production of phenylalanine-14C, leucine-1-14C, valine-1-14C, and glucose-1-14C-6-phosphate incubated in fresh or boiled human placenta homogenates in a saline phosphate buffer, pH 7.35, at 37ºC, gassed with 95% O2, 5% CO2, during 120 minutes.
Approximately 3.1 x 10-² %, 0.6 x 10-² %, and 0.28% 14C/gm of tissue were produced respectively from 14C-labeled phenylalanine, leucine, and glucose-6-phosphate.
The time at which maximum rate of 14CO2 production occurred (Tmax.) was 31.2, 29.1, and 30.2 minutes, respectively.
No 14CO2 production was obtained when valine-1-14C was incubated with fresh placenta homogenates, gassed with 95% O2, 5% CO2.
No 14CO2 production was detected when 14C-labeled phenylalanine, leucine, and glucose-6-phosphate were incubated with boiled human placenta homogenates.
A significantly increased 14CO2 production (p < 0.01) and a prolonged Tmax. from glucose-1-14C-6-phosphate were noted when incubated with 0.05 M Methylene blue and human placenta homogenates.
Conclusions:
1) Phenylalanine hydroxylase, glucose-6-phosphate
dehydrogenase, and decarboxylase of branched-chain keto acid involved
in the oxidative catabolism of phenylalanine, glucose-6-phosphate, and
leucine respectively might occur in human placenta.
2)
The fact that 14CO2 production can be measured from the oxidation of leucine-1-14C,
but not from the oxidation of valine-1-14C in human placenta homogenates,
suggests a possible occurrence of a specific enzyme in the degradative
pathway of leucine in this tissue.
3) Methylene blue stimulates
the oxidation of glucose-6-phosphate via Pentose phosphate pathway in
human placenta tissue.
4) Dependency of oxidation
to CO2 of the 1-carbon of phenylalanine in the presence of phenylalanine
hydroxylase, of the 1-carbon of glucose-6-phosphate in the presence of
glucose-6-phosphate dehydrogenase, and of the 1-carbon of leucine in the
presence of decarboxylase of branched-chain keto acid of leucine, suggests
that 14CO2 production from phenylalanine-1-14C glucose-1-14C-6-phosphate,
and leucine-1-14C incubated with human placenta homogenates might be a
measure of enzyme activities and thus such measurements might be useful
for screening populations for phenylketonuria (PKU), glucose-6-phosphate
dehydrogenase deficiency, and maple-syrup-urine disease at birth in vitro.
Journal of Nuclear Medicine, 12: 468-469, 1971.
Macel Laplante was a Ph.D graduate student in Nuclear Medicine and Radiobiology, University of Sherbrooke Medical School, Sherbrooke, Québec, Cannada.
