The reciprocal exclusion by L-dopa (L-3,4-dihydroxyphenylalanine) and L-tyrosine of their incorporation as single units into a soluble rat brain protein.
Several compounds, structurally and metabolically related to phenylalanine and tyrosine, were tested for their effects on the incorporations of phenylalanine and tyrosine as single units into a protein of the soluble subcellular fraction of rat brain. Of the compounds tested, only L-dopa (L-3,4-dihydroxyphenylalanine) inhibited these incorporations. Further, L-dopa was incorporated into a protein of the same fraction in such a way that it excluded the incorporation of tyrosine as a single unit. Conversely, tyrosine inhibited and excluded the incorporation of L-dopa. The incorporation of L-dopa required ATP (apparent Km = 0.23mM), KCl (apparent Km = 20mM) and MgCl2 (optimal concentration range, 5-16mM). These requirements were similar to those previously determined for the incorporation of tyrosine and phenylalanine. The inactivation rate of the enzymic systems for L-tyrosine and L-dopa incorporations, when kept at 37 degrees C, was the same for both amino acids (half-life = 80 min). It is suggested that the acceptor for the incorporation of dopa is the same as that for the incorporation of tyrosine.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D004295:Dihydroxyphenylalanine / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D009994:Osmolar Concentration; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*
D009419:Nerve Tissue Proteins; D014443:Tyrosine; D010649:Phenylalanine; D004295:Dihydroxyphenylalanine; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D008274:Magnesium