Tetrahydrobiopterin and total biopterin content of neuroblastoma (N1E-115, N2A) and pheochromocytoma (PC-12) clones and the dependence of catecholamine synthesis on tetrahydrobiopterin concentration in PC-12 cells.

Tetrahydrobiopterin content was determined in several clonal cell lines by reversed-phase HPLC and subsequent electrochemical detection. The same chromatography system was used to determine the total biopterin (tetrahydrobiopterin and 7,8-dihydrobiopterin) by fluorescence detection. The catecholamine-producing clones neuroblastoma N1E-115 and pheochromocytoma PC-12 contained 96 and 60 ng tetrahydrobiopterin/mg protein, respectively. The corresponding amount for the neuroblastoma clone N2A was 36 ng/mg protein. The tetrahydrobiopterin content in C-6 glioma cells was below the limit of detection. The total biopterin is about 20% above the tetrahydrobiopterin content. Tetrahydrobiopterin and biopterin from the cells were identified by coelution with standard solutions and by potential-current relationship or emission and excitation spectra, respectively. Addition of 2,4-diamino-6-hydroxypyrimidine, an inhibitor of biopterin synthesis from GTP, to the culture medium of PC-12 cells resulted in a dose-dependent decrease of tetrahydrobiopterin and total biopterin content within 4 h, suggesting that the cells are capable of synthesising the biopterin which was found. A decrease in intracellular tetrahydrobiopterin levels by different concentrations of 2,4-diamino-6-hydroxypyrimidine reduces the cellular production of dihydroxyphenylalanine after inhibition of aromatic L-amino acid decarboxylase, indicating that the concentration of tetrahydrobiopterin might be a limiting factor for catecholamine synthesis in catecholamine-producing cells.