Mechanism of thyroxine-mediated oxidation of reduced nicotinamide adenine dinucleotide in the peroxidase-hydrogen peroxide system

Biochemistry ◽  
1977 ◽  
Vol 16 (9) ◽  
pp. 1921-1926 ◽  
Author(s):  
Kiyoshige Takayama ◽  
Minoru Nakano
Keyword(s):  
Hydrogen Peroxide ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine ◽  
Reduced Nicotinamide Adenine Dinucleotide ◽  
Mediated Oxidation

scholarly journals The inactivation of phenylalanine hydroxylase by 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine and the aerobic oxidation of the latter. The effects of catalase, dithiothreitol and reduced nicotinamide–adenine dinucleotide

1971 ◽  
Vol 125 (2) ◽  
pp. 563-568 ◽  
Author(s):  
A. Jakubovič ◽  
L. I. Woolf ◽  
E. Chan-Henry
Keyword(s):  
Hydrogen Peroxide ◽  
Nicotinamide Adenine Dinucleotide ◽  
Phenylalanine Hydroxylase ◽  
Liver Extract ◽  
Aerobic Oxidation ◽  
Organic Peroxide ◽  
Nicotinamide Adenine ◽  
Oxidation In Air ◽  
Reduced Nicotinamide Adenine Dinucleotide

1. Phenylalanine hydroxylase is inhibited by its cofactor, 6,7-dimethyltetrahydropterin. The rate of inactivation, which is irreversible, increases with the concentration of cofactor. 2. Catalase, in sufficient amount relative to cofactor, prevents this inactivation. More tyrosine is formed in the presence of added catalase. 3. Dithiothreitol in the presence of liver extract also prevents inactivation of the enzyme by the cofactor and stimulates hydroxylation of phenylalanine, probably by protecting the cofactor from oxidation and regenerating it from a dihydropterin reaction product. Dithiothreitol restores linearity of rate at very low enzyme concentrations. 4. Dimethyltetrahydropterin is unstable when the solution is exposed to air but is stabilized by dithiothreitol the aerobic oxidation of which is greatly accelerated by dimethyltetrahydropterin. 5. NADH together with liver extract stabilizes the cofactor but not phenylalanine hydroxylase. 6. It is suggested that either hydrogen peroxide or an organic peroxide formed by oxidation in air of the cofactor is the substance attacking phenylalanine hydroxylase, dithiothreitol and cofactor.

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