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Activity of synthetic enzymes of tetrahydrobiopterin in the human placenta

Authors :
Yuichiro Nakai
Haruo Shintaku
Daisuke Tachibana
Junko Nishio
Naoko Iwanaga
Seiichi Yamamasu
Osamu Ishiko
Source :
International Journal of Molecular Medicine.
Publication Year :
2004
Publisher :
Spandidos Publications, 2004.

Abstract

Tetrahydrobiopterin (BH 4 ) is an essential co-factor for nitric oxide (NO) synthase (NOS) and regulates the production of NO, or endothelium derived relaxation factor. Although NOS is highly expressed in the placenta and NO plays a critical role in the regulation of feto-placental circulation, the mechanism maintaining the level of BH 4 is not known. To investigate the de novo synthesis of BH 4 in the human placenta, the activity of guanosine triphosphate cyclo-hydrolase I (GTPCH), 6-pyruvoyltetrahydropterin synthase (PTPS), and sepiapterin reductase (SR) in the chorionic tissue during the first, second and third trimester of pregnancy was analyzed. GTPCH activity was the lowest of the three enzymes and became negligible after the second trimester. There was no significant change in PTPS activity throughout pregnancy. Although SR activity decreased significantly after the second trimester, the levels remained abundant throughout pregnancy. These results showed that GTPCH is a rate-limiting enzyme and the total activity of the de novo synthesis of BH 4 is negligible in the mature placenta after the second trimester when fetal growth is accelerated. The present study suggests that the level of BH 4 in the placenta depends principally on the system other than de novo synthesis. The salvage pathway is considered the most potent system, which is formed by the transfer of the substrates from the fetus and their enzymatic conversion to BH 4 in the placenta.

Details

ISSN :
1791244X and 11073756
Database :
OpenAIRE
Journal :
International Journal of Molecular Medicine
Accession number :
edsair.doi.dedup.....730b1a85b4b84e6fc5eaec9a1b5ee949
Full Text :
https://doi.org/10.3892/ijmm.13.1.117