This family consists of several bacterial malonate decarboxylase delta subunit (MdcD) proteins. Malonate decarboxylase of Klebsiella pneumoniae consists of four different subunits and catalyzes the conversion of malonate plus H+ to acetate and CO2. The catalysis proceeds via acetyl and malonyl thioester residues with the phosphribosyl-dephospho-CoA prosthetic group of the acyl carrier protein (ACP) subunit. MdcC is the (apo) ACP subunit. The family also contains the CitD family of citrate lyase acyl carrier proteins.