RRC ID 38654
著者 Hatakeyama K, Harada T, Kagamiyama H.
タイトル IMP dehydrogenase inhibitors reduce intracellular tetrahydrobiopterin levels through reduction of intracellular GTP levels. Indications of the regulation of GTP cyclohydrolase I activity by restriction of GTP availability in the cells.
ジャーナル J Biol Chem
Abstract GTP cyclohydrolase I exhibits a positive homotropic cooperative binding to GTP, which raises the possibility of a role for GTP in regulating the enzyme reaction (Hatakeyama, K., Harada, T., Suzuki, S., Watanabe, Y., and Kagamiyama, H. (1989) J. Biol. Chem. 264, 21660-21664). We examined whether or not the intracellular GTP level is within the range of affecting GTP cyclohydrolase I activity, using PC-12 rat pheochromocytoma and IMR-32 human neuroblastoma cells. Since GTP cyclohydrolase I was the rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin in these cell lines, the intracellular activities of this enzyme were reflected in the tetrahydrobiopterin contents. We found that the addition of guanine or guanosine increased GTP but not tetrahydrobiopterin in these cells. On the other hand, three IMP dehydrogenase inhibitors, tiazofurin, 2-amino-1,3,4-thiadiazole, and mycophenolic acid, decreased both GTP and tetrahydrobiopterin in a parallel and dose-dependent manner, and these effects were reversed by the simultaneous addition of guanine or guanosine. There was no evidence suggesting that these inhibitors inhibited other enzymes involved in the biosynthesis and regeneration of tetrahydrobiopterin. Comparing intracellular activities of GTP cyclohydrolase I in the inhibitor-treated cells with its substrate-velocity curve, we estimated that the intracellular concentration of free GTP is 150 microM at which point the activity of GTP cyclohydrolase I is elicited at its maximum velocity. Below this GTP concentration, GTP cyclohydrolase I activity is rapidly decreased. Therefore GTP can be a regulator for tetrahydrobiopterin biosynthesis.
巻・号 267(29)
ページ 20734-9
公開日 1992-10-15
PII S0021-9258(19)36747-X
PMID 1356983
MeSH Animals Antineoplastic Agents / pharmacology* Biopterin / analogs & derivatives* Biopterin / metabolism GTP Cyclohydrolase / metabolism* Guanine / pharmacology* Guanosine / pharmacology* Guanosine Triphosphate / metabolism* Humans IMP Dehydrogenase / antagonists & inhibitors* Kinetics Mycophenolic Acid / pharmacology* Neuroblastoma PC12 Cells Ribavirin / analogs & derivatives* Ribavirin / pharmacology Thiadiazoles / pharmacology* Tumor Cells, Cultured
IF 4.238
引用数 56
WOS 分野 BIOCHEMISTRY & MOLECULAR BIOLOGY
リソース情報
ヒト・動物細胞 PC-12(RCB0009)