2-pyrone-4,6-dicarboxylic acid (PDC) hydrolase hydrolyzes PDC to yield 4-oxalomesaconic acid (OMA) or its tautomer, 4-carboxy-2-hydroxymuconic acid (CHM). This reaction is part of the protocatechuate (PCA) 4,5-cleavage pathway. PCA is one of the most important intermediate metabolites in the bacterial pathways for various phenolic compounds, including lignin, which is the most abundant aromatic material in nature.