The tyrosine-dependent oxidation of tetrahydropterins by lysolecithin-activated rat liver phenylalanine hydroxylase.

Evidence for the formation of the 4a-carbinolamine during the tyrosine-dependent oxidation of tetrahydrobiopterin by rat liver phenylalanine hydroxylase.

In the presence of phenylalanine and molecular oxygen, activated phenylalanine hydroxylase catalyzes the oxidation of tetrahydrobiopterin. The oxidation of this tetrahydropterin cofactor also proceeds if the substrate, phenylalanine, is replaced by its product, tyrosine, in the initial reaction mixture. These two reactions have been defined as coupled and uncoupled, respectively, because in the...

Tetrahydropterin oxidation without hydroxylation catalyzed by rat liver phenylalanine hydroxylase.

Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat.

The plasma concentration of phenylalanine and tyrosine decreases in normal rats during the first few postnatal days; subsequently, the concentration of phenylalanine remains more or less constant, whereas that of tyrosine exhibits a high peak on day 13. The basal concentrations of the two amino acids were not altered by injections of thyroxine or cortisol, except in 13-day-old rats, when an inj...

Thermodynamic characterization of the binding of tetrahydropterins to phenylalanine hydroxylase.

Phenylalanine hydroxylase (PAH) is the key enzyme in the catabolism of L-Phe. The natural cofactor of PAH, 6R-tetrahydrobiopterin (BH4), negatively regulates the enzyme activity in addition to being an essential cosubstrate for catalysis. The analogue 6-methyltetrahydropterin (6M-PH4) is effective in catalysis but does not regulate PAH. Here, the thermodynamics of binding of BH4 and 6M-PH4 to h...

The activation of rat liver phenylalanine hydroxylase by limited proteolysis, lysolecithin, and tocopherol phosphate. Changes in conformation and catalytic properties.

Pure phenylalanine hydroxylase from rat liver can be activated by limited proteolysis with alpha-chymotrypsin. As with most other types of activation of this enzyme, including activation by exposure to lysolecithin, the increase in activity is expressed in the presence of the naturally occurring pterin cofactor, tetrahydrobiopterin, but not in the presence of synthetic pterin cofactors such as ...