Mitochondrial protein that acts as an oxaloacetate decarboxylase (ODx), catalyzing the decarboxylation of oxaloacetate (OAA) to pyruvate and CO(2), and as such is likely a regulatory enzyme in the TCA cycle (PubMed:25575590, PubMed:30348641). Also displays acylpyruvase activity, being able to hydrolyze acetylpyruvate and fumarylpyruvate in vitro (PubMed:21878618, PubMed:30348641). Exhibits only a weak hydrolase activity on methylacetopyruvate and acetylacetone, and no activity toward acetoacetyl-CoA (PubMed:21878618).