CHI- C-CH- -CoA ATP ADP+ P Acetvl-CoA Malonyl-CoA + HcO biotin Trans carboXvlase carboxvlase arm side arm O-C Biotin camier Biotin Biotin Biotin O NH Acetyl-CoA carboxylase carner protein catalyzes the two-step carboxylation reaction Transcarboxylase of acetvl-CoA in two S-CoA active sites Acetyl-COA S-CoA Malonyl-CoAbiotin carboxylase Trans￾carboxylase Acetyl-CoA carboxylase catalyzes the two-step carboxylation reaction of acetyl-CoA in two active sites