JBC, Vol. 251, Issue 22, 6901-6908, Nov, 1976
Properties of phenylalanine hydroxylase of cultured hepatoma cells
D. F. Haggerty, G. Popjak and P. L. Young
The kinetic and immunologic properties of phenylalanine hydroxylase of
adult rat liver were compared to the properties of the similar enzyme
present in cultured H4-II-E-C3 hepatoma cells. The enzymes from the two
sources could not be distinguished by the Km values for either
phenylalanine or 6,7-dimethyltetrahydropterin. Analysis by double
immunodiffusion showed that phenylalanine hydroxylase from the two sources
had identical immunologic determinants, but immunotitrations revealed a
small but significant difference between the enzyme of the normal adult rat
liver and the enzyme of cultured hepatoma cells. The results of double
immunodiffusion and immunotitration experiments indicated also that the
increased levels of phenylalanine hydroxylase seen in the hepatoma cells
grown in the presence of hydrocortisone resulted from the accumulation of
enzyme protein, but it could not be decided whether this accumulation
resulted from an increased rate of synthesis or decreased rate of
degradation.
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