Limited denaturation stimulates tetrahydrobiopterin-dependent activity of rat liver phenylalanine hydroxylase

1990 ◽  
pp. 656-659
Keyword(s):  
Rat Liver ◽  
Phenylalanine Hydroxylase ◽  
Dependent Activity

High Protein Diet and Phenylalanine Hydroxylase Activities in Rats

Pteridines ◽  
1989 ◽  
Vol 1 (4) ◽  
pp. 235-238 ◽  
Author(s):  
Michael P. Carty ◽  
Edel Beirne ◽  
John Donlon
Keyword(s):  
Rat Liver ◽  
Phenylalanine Hydroxylase ◽  
High Protein Diet ◽  
High Protein ◽  
Protein Diet ◽  
Casein Diet ◽  
Dependent Activity ◽  
Liver And Kidney ◽  
Phenylalanine Metabolism

SummaryThe effects of a diet of 85% casein on the activities of the phenylalanine hydroxylases of rat liver and kidney have been compared. Whereas only the tetrahydrobiopterin-dependent activity of rat hepatic phenylalanine hydroxylase is significantly stimulated, both the tetrahydrobiopterin-dependent and the dimethyltetrahydropterin- dependent activities of the renal enzyme are significantly decreased, after five days of feeding a casein diet. The animals fed a high protein diet for seven days have an increased rate of phenylalanine catabolism in vivo, which is also reflected in increased flux of label from phenylalanine into glucose. The regulation of phenylalanine metabolism, under these conditions, is discussed.

scholarly journals Interaction with a monoclonal antibody alters the expression of co-operativity by phenylalanine hydroxylase from rat liver

1989 ◽  
Vol 257 (2) ◽  
pp. 383-388 ◽  
Author(s):  
M A Parniak ◽  
I G Jennings ◽  
R G H Cotton
Keyword(s):  
Monoclonal Antibody ◽  
Rat Liver ◽  
Phenylalanine Hydroxylase ◽  
Conformational Epitope ◽  
Enzyme Molecule ◽  
Phenylalanine Concentration ◽  
Naturally Occurring ◽  
Dependent Activity ◽  
Substrate Level ◽  
Maximal Binding

Phenylalanine hydroxylase purified from rat liver shows positive co-operativity in response to variations in phenylalanine concentration when assayed with the naturally occurring cofactor tetrahydrobiopterin. In addition, preincubation of phenylalanine hydroxylase with phenylalanine results in a substantial activation of the tetrahydrobiopterin-dependent activity of the enzyme. The monoclonal antibody PH-1 binds to phenylalanine hydroxylase only after the enzyme has been preincubated with phenylalanine and is therefore assumed to recognize a conformational epitope associated with substrate-level activation of the hydroxylase. Under these conditions, PH-1 inhibits the activity of phenylalanine hydroxylase; however, at maximal binding of PH-1 the enzyme is still 2-3 fold activated relative to the native enzyme. The inhibition by PH-1 is non-competitive with respect to tetrahydropterin cofactor. This suggests that PH-1 does not bind to an epitope at the active site of the hydroxylase. Upon maximal binding of PH-1, the positive co-operativity normally expressed by phenylalanine hydroxylase with respect to variations in phenylalanine concentration is abolished. The monoclonal antibody may therefore interact with phenylalanine hydroxylase at or near the regulatory or activator-binding site for phenylalanine on the enzyme molecule.

Comparison of Different Methods for the Determination of Phenylalanine Hydroxylase Activity in Rat Liver and Euglena gracilis

1984 ◽  
Vol 39 (7-8) ◽  
pp. 728-733 ◽  
Author(s):  
Rita M. Fink ◽  
Erich F. Elstner
Keyword(s):  
Rat Liver ◽  
Euglena Gracilis ◽  
Phenylalanine Hydroxylase ◽  
Hplc Method ◽  
Enzymic Activity ◽  
Hydroxylase Activity ◽  
Product Separation ◽  
Tyrosine Concentration ◽  
Layer Chromatography

Abstract Three different methods for the determination of phenylalanine hydroxylase activity have been compared: a) Differential photometric assay of the increase in tyrosine concentration in the presence of phenylalanine; b) Product separation by thin layer chromatography and scintillation counting of the [14C]tyrosine formed;c) HPLC separation and spectrofluorometric quantification of derivatized amino acids. A comparison of the activities of phenylalanine hydroxylase in rat liver and Euglena gracilis clearly showed that only rat liver contains this enzymic activity as shown by methods b) and c) although pseudo-activity of Euglena gracilis preparations was found during the spectrophotometric test a). The HPLC method proved to be the fastest, most reliable and convenient method for direct tyrosine determination and thus for measuring phenylalanine hydroxylase activity.

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