Biosynthesis of tetrahydrobiopterin by de novo and salvage pathways in adrenal medulla extracts, mammalian cell cultures, and rat brain in vivo.

Abstract

Communicated by George H. Hitchings, December 13, 1982 ABSTRACT Mammalian cells and tissues were found to have two pathways for the biosynthesis of tetrahydrobiopterin (BH4): (i) the conversion of GTP to BH4 by a methotrexate-insensitive de novo pathway, and (ii) the conversion of sepiapterin to BH4 by a pterin salvage pathway dependent on dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) activity. In a Chinese hamster ovary cell mutant lacking dihydrofolate reductase (DUKX-BII), endogenous formation of BH4 proceeds normally but, unlike the parent cells, these cells or extracts ofthem do not convert sepiapterin or 7,8-dihydrobiopterin to BH4. KB cells, which do not contain detectable levels of GTP cyclohydrolase or BH4 but do contain dihydrofolate reductase, readily convert sepiapterin to BH4 and this conversion is completely prevented by methotrexate. In supernatant fractions of bovine adrenal medulla, the conversion of sepiapterin to BH4 is completely inhibited by methotrexate. Similarly, this conversion in rat brain in vivo is methotrexate-sensitive. Sepiapterin and 7,8-dihydrobiopterin apparently do not enter the de novo pathway of BH4 biosynthesis and may be derived from labile intermediates which have not yet been characterized.

Mechanisms of H2O2-induced oxidative stress in endothelial cells

“…As was observed in rat aortic SMC Addition of L-sepiapterin in culture has been shown to salvage BH 4 (Nichol et al 1983), allowing for NOS production of NO rather then O 2 .-in the presence of ONOO -.…”

The genetics of exceptional longevity identifies new druggable targets for vascular protection and repair

“…Lack of functional co-factors, tetrahydrobiopterin (BH4) being the crucial one, impairs dimerization, with the consequent switch from NO generation to superoxide anions production, a process known as NOS uncoupling (32). BH4 oxidation generates dihydrobiopterin (BH2) that in turn contributes to uncoupling (33). Since BH2 competes with BH4…”

Tetrahydrobiopterin Inhibits PDGF-stimulated Migration and Proliferation in Rat Aortic Smooth Muscle Cells via the Nitric Oxide Synthase-independent Pathway

“…BH4 is commonly known to be an essential cofactor for NOS [1]. To examine whether the effect of BH4 on PDGF-increased migration involved NO, we analyzed the responses to L-NAME, a NOS inhibitor, in RASMCs treated with BH4 (100 μM).…”

“…Tetrahydrobiopterin (BH4) is an essential cofactor required for the activities of aromatic amino acid hydroxylase and all isoforms of nitric oxide synthase (NOS) [1,2]. BH4 is involved in neurotransmitter biosynthesis, glyceryl ether monooxygenase activity, and NOS activity [3].…”

“…Intracellular BH4 can be formed via biosynthesis, reproduction, and salvage pathways [4]. BH4 biosynthesis is initiated by GTP cyclohydrolase (GTPCH) in an NADPH-dependent reaction and continues through the production of 2 intermediates, namely, 7, 8-dihydroneopterin triphosphate and 6-pyruvoyl-5,6,7,8-tetrahydropterins, mediated by 6-pyruvoyltetrahydropterin synthase (PTPs) and sepiapterin reductase (SR) [1]. Moreover, BH4 can be reproduced from its oxidized forms, dihydrobiopterin (BH2) and quinoidin-BH2 (qBH2), by two other enzymes, dihydrofolate reductase (DHFR) and dihydrobiopterin reductase (DHPR), respectively [4,5].…”