Expression and regulation of rat 6-pyruvoyl tetrahydropterin synthase mRNA.

6-Pyruvoyl tetrahydropterin synthase catalyzes the second step in the biosynthesis of tetrahydrobiopterin. In the present study, the reverse transcription-polymerase chain reaction technique was used to clone a portion of 6-pyruvoyl tetrahydropterin synthase cDNA from rat pineal gland RNA. The sequence of this cDNA was found to be essentially identical to that previously reported for the rat liver. 6-Pyruvoyl tetrahydropterin synthase mRNA levels in various rat tissues, including the brain, were then analyzed by Northern blot and nuclease protection assay. A single 1.35 kb transcript of 6-pyruvoyl tetrahydropterin synthase mRNA was detected by Northern blot analysis in the rat adrenal gland, brain-stem, and liver. Quantitation by nuclease protection assay demonstrated that 6-pyruvoyl tetrahydropterin synthase mRNA was most abundant in the adrenal gland, kidney, and pineal gland (19.5-25.5 amol/microgram RNA). Relatively homogeneous levels of 6-pyruvoyl tetrahydropterin synthase mRNA were found in various brain regions including the cerebellum, substantia nigra and locus coeruleus (4.12-12 amol/microgram RNA). In the adrenal gland, 6-pyruvoyl tetrahydropterin synthase and tyrosine hydroxylase mRNAs were elevated between 3 and 4-fold 24 h after a single dose of reserpine (10 mg/kg), a treatment known to increase tetrahydrobiopterin levels in this tissue. This result suggests that although 6-pyruvoyl tetrahydropterin synthase is not believed to be rate-limiting in the tetrahydrobiopterin biosynthetic pathway, control of gene expression for this enzyme may play an essential role in regulating the synthesis of this important cofactor.