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1	Author	RitaM. Fink, ErichF. Elstner	Requires 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

2	Author	RitaM. Fink, ErichF. Elstner	Requires 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. 1.14.16.1.) 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