Decarboxylation-dependent transamination catalyzed by mammalian 3,4-dihydroxyphenylalanine decarboxylase.
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.
D000818:Animals; D004296:Dopa Decarboxylase / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008781:Methyltyrosines / Q000378:metabolism; D013379:Substrate Specificity; D013552:Swine; D000637:Transaminases / Q000378:metabolism*
D008781:Methyltyrosines; D000637:Transaminases; D004296:Dopa Decarboxylase