Figure 28.5 A schematic representation of a single chain of animal fatty acid synthase. (A) The arrangement of the catalytic activities present in a single polypeptide chain. (B) A cartoon of the dimer based on an x-ray crystallographic result. The ψMT and ψKR are inactive domains similar to methyl transferase and ketoreductase sequences. Although there are two domains for DH, only one is active. The inactive domains are presented in faded colors. Dotted lines outline domains for which the structure has not yet been determined. Abbreviations: KS, β-ketoacyl synthase; MAT, malonyl-acetyl transferase; DH, dehydratase; ψMT, methyl transferase (inactive); ψKR, ketoreductase (inactive); ER, enoyl reductase; KR, ketoreductase; ACP, acyl carrier protein; TE, thioesterase.