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  • Title: Decarboxylation-dependent transamination catalyzed by mammalian 3,4-dihydroxyphenylalanine decarboxylase.
    Author: O'Leary MH, Baughn RL.
    Journal: J Biol Chem; 1977 Oct 25; 252(20):7168-73. PubMed ID: 561784.
    Abstract:
    In addition to the usual decarboxylation, pig kidney 3,4-dihydroxyphenylalanine (dopa) decarboxylase catalyzes a decarboxylation-dependent transamination which converts dopa into 3,4-dihydroxyphenylacetaldehyde and sinultaneously converts enzyme-bound pyridoxal-P into pyridoxamine-P. Similar reactions occur when this enzyme acts on m-tyrosine, alpha-methyldopa, and alpha-methyl-m-tyrosine. The transamination occurs in about 0.02% of decarboxylations of dopa and m-tyrosine and in about 2% of decarboxylations of alpha-methyldopa and alpha-methyl-m-tyrosine. The fraction of decarboxylations proceeding by the transamination pathway is independent of pH. This reaction appears to result from a divergence in the normal mechanism of decarboxylation; the quinoid intermediate which is formed by decarboxylation of the substrate-pyridoxal-P-Schiff base ordinarily protonates on the alpha carbon of the amino acid, but protonation occasionally occurs at the benzylic carbon of the coenzyme, and this latter route leads to transamination.
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