(6R)-tetrahydrobiopterin increases the activity of tryptophan hydroxylase in rat raphe slices.
The effects of (6R)- and (6S)-tetrahydrobiopterin (BPH4), tetrahydroneopterin, and 6-methyltetrahydropterin on the activity of tryptophan hydroxylase were investigated in rat raphe slices. The activity of tryptophan hydroxylase was estimated by measurement of 5-hydroxytryptophan (5-HTP) formation under inhibition of aromatic L-amino acid decarboxylase with use of HPLC-fluorometric detection. (6R)-BPH4 (the naturally occurring form) at 42 microM, tetrahydroneopterin at 50 microM, and 6-methyltetrahydropterin at 100 microM increased tryptophan hydroxylase activity to 350, 145, and 146% of control values, respectively. (6S)-BPH4, however, had no significant effects on tryptophan hydroxylase activity. These results suggest that tryptophan hydroxylase is subsaturating in vivo for the naturally occurring cofactor, (6R)-BPH4, and that the concentration of (6R)-BPH4 may play an important role for the regulation of tryptophan hydroxylase activity in vivo.
D006916:5-Hydroxytryptophan / Q000378:metabolism; D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D011622:Pterins / Q000494:pharmacology; D011903:Raphe Nuclei / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
D011622:Pterins; D001708:Biopterins; D006916:5-Hydroxytryptophan; C017523:6-methyltetrahydropterin; D014365:Tryptophan Hydroxylase; C003402:sapropterin