Presence of two polypeptide chains comprising fatty acid synthetase

Highly purified fatty acid synthetases of chicken and rat livers have molecular weights of 500,000 and dissociate in solutions of low ionic strength into subunits of molecular weight 250,000 with loss of synthetase activity. The subunits can be reassociated in phosphate buffer with full restoration of the activity. In the presence of sodium dodecyl sulfate or guanifine-HCl, the synthetases dissociate into polypeptide chains of molecular weight 220,000 as determined by sodium dodecyl sulfate-gel electrophoresis and sedimentation equilibrium. The polypeptide contains the 4-phosphopantetheine group and the [14C]acetyl and [4C]malonyl groups if the synthetases were prelabeled with [14C]acetyl-CoA and [14C]malonyl-CoA. Similar results were obtained with the synthetase from yeast, except the subunit has a molecular weight of 200,000. These observations indicate that the multi-catalytic activities of the synthetases and the acyl carrier protein are associated only with the two polypeptide chains. The findings suggest a novel structural organization for multienzyme complexes.