Tetrahydrobiopterin, a Cofactor for Rat Cerebellar Nitric Oxide Synthase, does not Function as a Reactant in the Oxygenation of Arginine

Studies with purified nitric oxide synthase from rat cerebellum have confirmed previous reports that product formation is enhanced by tetrahydrobiopterin [H4B; 6-(L-erythro-1,2-dihydroxypropyl)-5,6,7,8-tetrahydropterin]. The effect of the natural isomer, (6R)-H4B, is observed at extremely low (15 mo...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1991-08, Vol.88 (16), p.7091-7095
Main Authors: Giovanelli, John, Campos, Kenneth L., Kaufman, Seymour
Format: Article
Language:English
Subjects:
Amino Acid Oxidoreductases - isolation & purification
Amino Acid Oxidoreductases - metabolism
Analytical, structural and metabolic biochemistry
Animals
Arginine - metabolism
Biochemistry
Biological and medical sciences
Biopterins - analogs & derivatives
Biopterins - metabolism
Biopterins - pharmacology
Cerebellum - enzymology
Chromatography, Affinity
Chromatography, Ion Exchange
Enzymes
Enzymes and enzyme inhibitors
Fundamental and applied biological sciences. Psychology
Isomers
Kinetics
Macrophages
Male
Methotrexate - pharmacology
Miscellaneous
Nitric Oxide Synthase
Oxides
Protein Binding
Pterins
Rats
Rats, Inbred Strains
Reactants
Recycling
Thiols
Tissue oxygenation
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Summary:Studies with purified nitric oxide synthase from rat cerebellum have confirmed previous reports that product formation is enhanced by tetrahydrobiopterin [H4B; 6-(L-erythro-1,2-dihydroxypropyl)-5,6,7,8-tetrahydropterin]. The effect of the natural isomer, (6R)-H4B, is observed at extremely low (15 mol of product. Recycling of H4B was excluded by direct measurement during nitric oxide synthesis and by the demonstration that nitric oxide synthase is not inhibited by methotrexate. These combined results exclude H4B as a stoichiometric reactant and suggest that H4B enhances product formation by protecting enzyme activity against progressive loss. Preliminary studies indicate that the decreased activity in the absence of added H4B does not depend on catalytic turnover of the enzyme. The role of H4B may be allosteric or it may function to maintain some group(s) on the enzyme in a reduced state required for activity.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.88.16.7091