Tyrosine dopamine theory

The molecular mechanisms underlying the neurological deficits observed in individuals with PKU are unknown. However, decreased levels of neurotransmitters, including dopamine, are likely to play a major role in the observed cognitive disabilities (Diamond et al., 1994 Puglisi-Allegra et al., 2000 Pascucd et al., 2002). To date, two distinct theories have been proposed to explain the phenomenon (for review, see Dyer et al., 1996 and 2000). The tyrosine/dopamine theory predicts that cognitive difficulties stem from decreased levels of tyrosine, the... 

In the development of the theory that alkaloids derive from amino acids it was early suggested that the benzylisoquinoline bases could be formed by condensation of 2 molecules of tyrosine (CLI) via 3,4-di-hydroxyphenylalanine (CLII). Leete and Murril (229) have pointed out that if iV-norlaudanosoline (CLV R = H) is an intermediate in the biogenesis it could be formed by condensation of 1 mole of 3,4-dihydroxy-phenylethylamine (dopamine) (CLIII) and 1 mole of 3,4-dihydroxy-phenylpyruvic acid (CLI V) and the differential incorporation of each unit of tyrosine could be rationalized. When dopamine (CLIII) is the labeled material fed to the plant then the moiety of the suggested intermediate (CLV R = H) which derives from the pyruvic acid CLIV will not be radioactive. 

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