Decarboxylates ethylmalonyl-CoA, a potentially toxic metabolite, to form butyryl-CoA, suggesting it might be involved in metabolite proofreading (PubMed:22016388). Acts preferentially on (S)-ethylmalonyl-CoA but has also some activity on the (R)-isomer (By similarity). Also has methylmalonyl-CoA decarboxylase activity at lower level (By similarity).
