Homogentisate 1,2-dioxygenase; part of the L-tyrosine degradation gene cluster that mediates the biosynthesis of the brownish pigment pyomelanin as an alternative melanin (PubMed:19028908, PubMed:19715768, PubMed:22046314). The 4-hydroxyphenylpyruvate dioxygenase hppD catalyzes the conversion of 4-hydroxyphenylpyruvate to homogentisic acid (HGA) (PubMed:19028908, PubMed:22046314). The protein hmgX is crucial for this conversion and thus, probably functions as an accessory factor to mediate specific activity of hppD (PubMed:22046314). The homogentisate 1,2-dioxygenase hmgA is then involved in the cleavage of the aromatic ring of HGA and its conversion to 4-maleylacetoacetate (PubMed:19028908, PubMed:19715768). When hmgA activity is lowered by the cell wall integrity (CWI) signaling pathway, HGA accumulates and leads to the production of pyomelanin through benzoquinone acetic acid after oxidation and polymerization (PubMed:19715768). On the opposite, in non-stress conditions, both hppD and hmgA activities are balanced and HGA is degraded into 4-maleylacetoacetate (PubMed:19715768). 4-maleylacetoacetate is further converted to 4-fumarylacetoacetate by the maleylacetoacetate isomerase maiA, which is degraded into fumarate and acetoacetate by the fumarylacetoacetase fahA (Probable). homogentisate + O2 = 4-maleylacetoacetate + H(+) Growth under standard conditions leads to moderate phosphorylation of mpkA and hppD and hmgA activities are balanced leading further to degradation of HGA and formation of 4-maleylacetoacetate (PubMed:19715768). Cell wall stress, resulting in disturbance of balanced hppD and hmgA enzyme activity, (with reduced hmgA activity), leads to HGA accumulation that polymerizes to pyomelanin (PubMed:19715768). Amino-acid degradation; L-phenylalanine degradation; acetoacetate and fumarate from L-phenylalanine: step 4/6. Expression is induced by L-tyrosine (PubMed:19028908). Expression is positively regulated by the cluster-specific transcription factor hmgR (PubMed:22046314). Impairs growth on L-tyrosine as the sole carbon (PubMed:19028908). Leads to the accumulation of homogentisic acid (HGA) and its subsequent polymerization to pyomelanin (PubMed:19028908). Belongs to the homogentisate dioxygenase family.