The Subunit Structure of the Pyruvate‐Dehydrogenase Complex from Escherichia coli K‐12

It is shown that very likely the Escherichia coli K‐12 pyruvate dehydrogenase complex is not a unique entity in that the amount of pyruvate dehydrogenase component it contains can vary. A complex can be obtained from which “excess” pyruvate dehydrogenase component is removed and this complex, called core complex, has an entirely reproducible polypeptide chain composition. The core complex has a molecular weight of 3750000 ± 200000. In the core complex the dihydrolipoamide transacetylase component can consist of a polypeptide chain with a molecular weight of 80000 or of a number of fragments of this chain. Although fragmentation of the transacetylase need not influence the catalytic activity of the core complex it is operationally defined as that multienzyme complex which contains the transacetylase subunit with M r = 80000.