Pyruvate Dehyrogenase Component Subunit Structure of the <i>Escherichia coli</i> K 12 Pyruvate Dehydrogenase Complex

Abstract

The pyruvate dehydrogenase component of the Escherichia coli pyruvate dehydrogenase complex is shown to be a dimeric protein consisting of identical or very nearly identical polypeptide chains with a molecular weight 90 000 to 110 000. In reasonable agreement with data obtained by Reed and collaborators the native enzyme was found to be a species with a sedimention coefficient s ° 20, w = 9.8 S, a diffusion coefficent D ° 20, w = 4.4 × 10 −7 cm 2 /sec, and a molecular weight of 200 000 to 220 000. Amino acid analyses and analyses of tryptic peptides showed that the minimum chemical molecular weight is around 100 000. Serine was found as an N‐terminal residue but with poor yields. One carboxyl terminal sequence…Arg‐Leu‐Ala‐CO 2 H per 10 5 daltons protein was shown by carboxypeptidase degradation. The protein could be dissociated by a variety of methods into only one species of subunit. The molecular weight of this subunit was found, by dodecylsulfate polycrylamide‐gel electrophoresis and sedimentation equilibrium in various solvents, to be 90 000 to 110 000.