Catalyzes the condensation of two molecules of acetyl-CoA to produce acetoacetyl-CoA (PubMed:1685080, PubMed:26391388). Involved in solvent production (PubMed:1685080, PubMed:26391388). 2 acetyl-CoA = acetoacetyl-CoA + CoA Regulated by a redox-switch modulation. Reversibly inactivated by oxidative stress through the disulfide bond formation between two catalytic residues, Cys-88 and Cys-378, which enables the enzyme to protect its active site from oxygen radicals and be reactivated upon switching back to a reducing condition. Homotetramer. Belongs to the thiolase-like superfamily. Thiolase family.