J. Biol. Chem., Vol. 255, Issue 21, 10029-10032, Nov, 1980
Relationship between the substrate activation site and catalytic site of phenylalanine hydroxylase
R Shiman
Rat liver phenylalanine hydroxylase when activated with phenylalanine
becomes catalytically competent. In the experiments presented, the
stoichiometry of binding of phenylalanine to activated rat liver
phenylalanine hydroxylase was measured. It was found 1) that there is 1
phenylalanine activation site/subunit of catalytically active enzyme,
implying 4 activation sites/active phenylalanine hydroxylase molecule
(tetramer); 2) that tryptophan (which is also a substrate for this enzyme)
will not bind at the activation site, demonstrating that the activation
site and catalytic site of the enzyme are not identical; additional
indirect evidence suggests that the activation site and catalytic site of
the enzyme do not physically overlap at all; and 3) that lysolecithin
(which can also activate this enzyme) and phenylalanine do not appear to
directly compete for the same activation site. An amino acid analysis of
rat liver phenylalanine hydroxylase is presented; also, an addition to the
purification procedure for phenylalanine hydroxylase (Shiman, R., Gray, D.
W., and Pater, A. (1979) J. Biol. Chem. 254, 11300-11306) is described that
allows one to obtain electrophoretically homogeneous enzyme of apparently
100% purity.
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