Branched-chain alpha-keto acid dehydrogenase complex from bovine kidney: radial distribution of mass determined from dark-field electron micrographs

Biochemistry. 1989 Aug 22;28(17):6816-21. doi: 10.1021/bi00443a006.


Scanning transmission electron microscopy (STEM) was used to determine the radial distribution of mass within the bovine kidney branched-chain alpha-keto acid dehydrogenase complex (E1-E2) and its core enzyme, dihydrolipoamide acyltransferase (E2). The particle mass of E2 measured by STEM is (1.19 +/- 0.02) x 10(6). Assuming 24 subunits per E2 core, this value corresponds to a subunit molecular weight of (4.96 +/- 0.08) x 10(4), which agrees well with the subunit molecular weight estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 5.2 x 10(4) (Pettit et al., 1978) and that deduced from the gene sequence, 46,518 (Griffin et al., 1988). Thus, the STEM data reaffirms the 24-subunit model for this E2. Previous studies indicated that the E2 subunits contain an extended, outer lipoyl-bearing domain connected by a trypsin-sensitive segment to a compact, inner catalytic domain. The assemblage of 24 inner domains comprises a cubelike inner core. The quantity and spatial distribution of mass determined from STEM images for the E2 inner core are consistent with this model. The lipoyl-bearing domains are shown to occupy a zone defined by radii of 80-130 A over which the lipoyl moiety may range. This zone overlaps the positions of the 24 branched-chain alpha-keto acid dehydrogenase (E1) molecules, which apparently are located on the of the cubelike inner core.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)
  • Animals
  • Cattle
  • Ketone Oxidoreductases* / isolation & purification
  • Kidney / enzymology*
  • Macromolecular Substances
  • Microscopy, Electron / methods
  • Microscopy, Electron, Scanning / methods
  • Models, Structural
  • Molecular Weight
  • Multienzyme Complexes* / isolation & purification
  • Protein Conformation


  • Macromolecular Substances
  • Multienzyme Complexes
  • Ketone Oxidoreductases
  • 3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)