Catalyzes the conversion of acetoacetate to acetone and carbon dioxide. acetoacetate + H(+) = acetone + CO2 kcat is 1560 sec(-1) (PubMed:8555196). kcat is 165 sec(-1) (PubMed:19458715). Optimum pH is 5.95. Homododecamer. By linear fatty acids (up to butyrate). Lys-116 may be involved in the precise positioning of the nucleophilic Lys-115. Belongs to the ADC family.