The enzyme, characterized from the bacterium Amycolatopsis mediterranei, is involved in biosynthesis of the nonproteinogenic amino acid (S)-3,5-dihydroxyphenylglycine, a component of the vancomycin-type antibiotic balhimycin.
diketyl-CoA and triketyl-CoA are confirmed to be the intermediates in the enzyme catalyzed synthesis of (3,5-dihydroxyphenylacetyl)-CoA. Polyketone intermediates alternate between the Cys160 residue and CoA through transthioesterification reactions, in which the chain is elongated by enolate attack on the thioester carbon of the enzyme-bound (poly)ketide intermediate by decarboxylation in malonyl-CoA or polyketide-CoA. Polyketone cyclization likely arises on CoA but not on the enzyme. Experimental data suggest that cyclization of linear tetraketidyl-CoA occurs in concert with or before decarboxylation of the terminal carboxyl group
kcat/Km for malonyl-CoA is 0.16% compared to the kcat/Km-value of the wild-type enzyme. The mutant shows an increased partition ratio for malonyl-CoA decarboxylation to acetyl-CoA vs condensation to 3,5-dihydroxyphenylacetyl-CoA, reflecting more uncoupling in the mutant enzyme