Decarboxylates ethylmalonyl-CoA, a potentially toxic metabolite, to form butyryl-CoA, suggesting it might be involved in metabolite proofreading. Acts preferentially on (S)-ethylmalonyl-CoA but has also some activity on the (R)-isomer. Also has methylmalonyl-CoA decarboxylase activity at lower level.
Subcellular locations: Cytoplasm, Cytosol