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1984 (2)
1Author    RitaM. Fink, ErichF. ElstnerRequires cookie*
 Title    Comparison of Different Methods for the Determination of Phenylalanine Hydroxylase Activity in Rat Liver and Euglena gracilis  
 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 spectrophoto-metric 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. 
  Reference    Z. Naturforsch. 39c, 728—733 (1984); received January 27/April 14 1984 
  Published    1984 
  Keywords    Phenylalanine Hydroxylase, Rat Liver, Euglena gracilis, Tyrosine Determination 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0728.pdf 
 Identifier    ZNC-1984-39c-0728 
 Volume    39 
2Author    RitaM. Fink, ErichF. ElstnerRequires cookie*
 Title    Studies on the Possible Mechanism of Inactivation of Phenylalanine Hydroxylase by Destructive Oxygen Species  
 Abstract    The enzymic hydroxylation of phenylalanine by phenylalanine hydroxylase (E.C. in vitro is dependent on the presence of hydrogen peroxide removing processes. The loss of phenylalanine hydroxylase activity can be prevented to the same extent by catalase as well as the presence of optimized amounts of both peroxidase and superoxide dismutase. Peroxidase alone exhibited only two third of the maximal protective effect of catalase whereas superoxide dismutase alone was not able to exert any protective influence on phenylalanine hydroxylase. These findings suggest that the termination of phenylalanine hydroxylation in the absence of hydrogen peroxide removing reactions is probably due to destructive oxygen species generated at the active site iron of phenylalanine hydroxylase in the presence of H 20 2 and the tetrahydropterin cofactor. 
  Reference    Z. Naturforsch. 39c, 734—737 (1984); received April 24 1984 
  Published    1984 
  Keywords    Phenylalanine Hydroxylase, Rat Liver, Inactivation Mechanism, Destructive Oxygen Species 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0734.pdf 
 Identifier    ZNC-1984-39c-0734 
 Volume    39