Studies in several laboratories (l-4) have established that isolated tissues growing or surviving in vitro require both phenylalanine and tyrosine. This finding is in marked contrast to the well known sparing effect of tyrosine on the phenylalanine requirement of the whole animal (5-7). In the latter case, this sparing effect has been attributed (8) to the action of “phenylalanine hydroxylase,”...

Volume 5 • Issue 6 • 1000e125 J Genet Syndr Gene Ther ISSN: 2157-7412 JGSGT, an open access journal Hyperphenylalaninemias (HPAs; OMIM 261600) are related to phenylalanine hydroxylase (PAH; OMIM *612349) deficiency; a hepatic enzyme, and are characterized by moderate and/or high levels of the amino acid phenylalanine and reduction of tyrosine. High levels of phenylalanine and low of tyrosine ch...

Membrane-permeable derivatives of cyclic AMP (cAMP) produced concentration-dependent increases in activity of tyrosine hydroxylase (L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2) in membrane-limited nerve endings (synaptosomes) prepared from three regions of rat brain. Increased hydroxylation occurred even after preincubation and removal of dibutyryl cycl...

The evidence presented shows that in vivo, in adult well fed rats, 20-4576 of liver phenylalanine hydroxylase is in an inactive state. This enzyme can be activated in a liver extract by addition of iron (II) and dithiothreitol and in situ by perfusion of rat liver with a defined medium. Activation during perfusion is not dependent on protein synthesis or affected by amino acid levels; activatio...