Membrane-bound phenylalanine hydroxylase of human liver.
Phenylalanine hydroxylase (EC 1.14.16.1) antigen and activity have been identified among proteins extracted with a buffer containing 0.4% Triton X-100 from adult human liver bioptate fraction, which was sedimented at 105,000 x g (n = 4). This enzyme fraction was designated as a 'membrane-bound form of phenylalanine hydroxylase'. It amounted to 5-15% of phenylalanine hydroxylase activity and 15-25% of phenylalanine hydroxylase antigen content. After immunoblotting two-dimensional gels, the soluble (cytoplasmic) form of phenylalanine hydroxylase antigen displayed three spots: one spot corresponded to the L-subunit with a molecular weight of 55,000, the two other spots corresponded to the H-subunit with a molecular weight of 57,000. Only the L-subunit was revealed in the membrane-bound enzyme form. Both phenylalanine hydroxylase activity and antigen were also demonstrated in extracts from human embryonic livers (n = 7). However, in this case the membrane-bound phenylalanine hydroxylase amounted to 85% of the antigen content. Subunit compositions of the enzymes were similar in adult and embryonic livers. The differences in the subunit compositions and enzyme activities of membrane-bound and cytoplasmic forms of phenylalanine hydroxylase in adults and embryos may be due to other functions of this enzyme in the hepatocyte membrane.
Chestkov
V V
VV
Institute of Medical Genetics, Academy of Medical Sciences, Moscow, Russia.
Laptev
A V
AV
Shishkin
S S
SS
D000328:Adult; D000368:Aged; D001324:Autoantigens / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D007120:Immunochemistry; D008099:Liver / Q000196:embryology / Q000201:enzymology*; D008297:Male; D008565:Membrane Proteins / Q000032:analysis*; D008875:Middle Aged; D010651:Phenylalanine Hydroxylase / Q000276:immunology / Q000378:metabolism*
D001324:Autoantigens; D008565:Membrane Proteins; D010651:Phenylalanine Hydroxylase