Properties and subunit composition of the pig heart 2-oxoglutarate dehydrogenase.

The 2-oxoglutarate dehydrogenase, one of the component enzymes of the 2-oxoglutarate dehydrogenase complex, has been highly purified. The enzyme has a sedimentation coefficient (s&~) of 10.3 S and diffusion coefficient (&o,~) of 3.92 X lo-’ cm2 s-l. The weight average molecular weight was estimated to be about 216,000 from the sedimentation equilibrium data. The content of right-handed LY helix in the enzyme molecule was estimated to be about 34% by both optical rotatory dispersion and circular dichroism. The enzyme was found to contain 1 molecule of protein-bound thiamine-PP per mole; some other kinetic and protein chemical properties are also reported. In 6 M guanidine hydrochloride (pH 8.0), the enzyme was dissociated into its subunits and the molecular weight of subunit was estimated to be 97,000 from the sedimentation equilibrium data. On polyacrylamide gel electrophoresis in sodium dodecyl sulfate the enzyme was dissociated into its subunits with an estimated molecular weight of 113,000. The results indicate that 1 molecule of 2-oxoglutarate dehydrogenase consists of two similar subunits, which contains NH&erminal alanine.