Competition for Tetrahydrobiopterin between Phenylalanine Hydroxylase and Nitric Oxide Synthase in Rat Liver*

Tetrahydrobiopterin (BH4) is an important cofactor for two hepatic enzymes, inducible nitric oxide synthase (iNOS) and phenylalanine hydroxylase (PAH), and competition for BH4 between the two enzymes might limit hepatic iNOS or PAH activity. To test this hypothesis, we determined whether conversion of phenylalanine to tyrosine was modified by changes in NO synthase activity, and conversely whether NO synthesis was limited by the rate of phenylalanine conversion to tyrosine in rat hepatocytes and perfused livers. NO production was decreased only slightly, when flux through PAH was maximized in isolated perfused livers, and in isolated hepatocytes only when BH4 synthesis was inhibited. Increases in NO synthesis did not reduce tyrosine formation from phenylalanine. Phenylalanine markedly increased biopterin synthesis, whereas arginine had no effect. Thus, basal BH4 synthesis appears to be adequate to support iNOS activity, whereas BH4 synthesis is increased to support PAH activity.

[1]  P. Robbins,et al.  Expression of human inducible nitric oxide synthase in a tetrahydrobiopterin (H4B)-deficient cell line: H4B promotes assembly of enzyme subunits into an active dimer. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[2]  L. Mitnaul,et al.  Coordinate regulation of tetrahydrobiopterin turnover and phenylalanine hydroxylase activity in rat liver cells. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[3]  D. W. Gray,et al.  Regulation of rat liver phenylalanine hydroxylase. III. Control of catalysis by (6R)-tetrahydrobiopterin and phenylalanine. , 1994, The Journal of biological chemistry.

[4]  S. Hoffman,et al.  Nitric oxide-mediated antiplasmodial activity in human and murine hepatocytes induced by gamma interferon and the parasite itself: enhancement by exogenous tetrahydrobiopterin , 1994, Infection and immunity.

[5]  C. Nathan,et al.  Regulation of biosynthesis of nitric oxide. , 1994, The Journal of biological chemistry.

[6]  E. Werner,et al.  The pteridine binding site of brain nitric oxide synthase. Tetrahydrobiopterin binding kinetics, specificity, and allosteric interaction with the substrate domain. , 1994, The Journal of biological chemistry.

[7]  G. Miotto,et al.  Multiphasic control of proteolysis by leucine and alanine in the isolated rat hepatocyte. , 1994, The American journal of physiology.

[8]  A. Nussler,et al.  Differential induction of nitric oxide synthase in hepatocytes during endotoxemia and the acute-phase response. , 1994, Archives of surgery.

[9]  K. Baek,et al.  Macrophage nitric oxide synthase subunits. Purification, characterization, and role of prosthetic groups and substrate in regulating their association into a dimeric enzyme. , 1993, The Journal of biological chemistry.

[10]  H. Kagamiyama,et al.  Feedback regulation mechanisms for the control of GTP cyclohydrolase I activity. , 1993, Science.

[11]  S. Gross,et al.  Tetrahydrobiopterin synthesis. An absolute requirement for cytokine-induced nitric oxide generation by vascular smooth muscle. , 1992, The Journal of biological chemistry.

[12]  F. Murad,et al.  Regulation and subcellular location of nitrogen oxide synthases in RAW264.7 macrophages. , 1992, Molecular pharmacology.

[13]  E. Werner,et al.  Tetrahydrobiopterin-dependent formation of endothelium-derived relaxing factor (nitric oxide) in aortic endothelial cells. , 1992, The Biochemical journal.

[14]  S. Kaufman,et al.  Tetrahydrobiopterin, a cofactor for rat cerebellar nitric oxide synthase, does not function as a reactant in the oxygenation of arginine. , 1991, Proceedings of the National Academy of Sciences of the United States of America.

[15]  T. Billiar,et al.  Effect of exogenous and endogenous nitric oxide on mitochondrial respiration of rat hepatocytes. , 1991, The American journal of physiology.

[16]  E. Werner,et al.  Tetrahydrobiopterin-dependent formation of nitrite and nitrate in murine fibroblasts , 1990, The Journal of experimental medicine.

[17]  T. Billiar,et al.  Inducible cytosolic enzyme activity for the production of nitrogen oxides from L-arginine in hepatocytes. , 1990, Biochemical and biophysical research communications.

[18]  S. Tannenbaum,et al.  Analysis of nitrate, nitrite, and [15N]nitrate in biological fluids. , 1982, Analytical biochemistry.

[19]  D. W. Gray,et al.  Substrate activation of phenylalanine hydroxylase. A kinetic characterization. , 1980, The Journal of biological chemistry.

[20]  T. Fukushima,et al.  Analysis of reduced forms of biopterin in biological tissues and fluids. , 1980, Analytical biochemistry.

[21]  S. Kaufman Studies on the mechanism of the enzymatic conversion of phenylalanine to tyrosine. , 1959, The Journal of biological chemistry.

[22]  S. Kaufman,et al.  Further studies on the phenylalanine-hydroxylation cofactor. , 1959, The Journal of biological chemistry.

[23]  D. Benos,et al.  Polarization-dependent apical membrane CFTR targeting underlies cAMP-stimulated Cl- secretion in epithelial cells. , 1994, The American journal of physiology.

[24]  N. Sakai,et al.  Tetrahydrobiopterin is required for cytokine-induced nitric oxide production in a murine macrophage cell line (RAW 264). , 1993, Molecular pharmacology.

[25]  S. Kaufman New tetrahydrobiopterin-dependent systems. , 1993, Annual review of nutrition.

[26]  P. Seglen Preparation of isolated rat liver cells. , 1976, Methods in cell biology.