Sizing of bovine heart and kidney pyruvate dehydrogenase complex and dihydrolipoyl transacetylase core by quasielastic light scattering

Quasielastic light scattering (QELS) measurements on several preparations of bovine heart and kidney pyruvate dehydrogenase complex yielded hydrodynamic radii (rH values) ranging from 25.7 to 30 nm. Gel filtration chromatography removed stable aggregates and generated preparations that gave essentially the same rH values of 24.3 +/- 0.6 nm for both complexes. The data were characteristic of a monodisperse system and agree with estimates using cryoelectron microscopy [Wagenknecht et al. (1991) J. Biol. Chem. 266, 24650-24656]. The equivalent hydrodynamic sizes for the heart and kidney complex indicate that the larger number of pyruvate dehydrogenase components in the heart complex (M(r) congruent to 9 x 10(6)) than the kidney complex (M(r) congruent to 7.5 x 10(6)) associate without radial expansion of the heart complex. That accommodation of additional mass is consistent with the space available since even in the more massive complex greater than 80% of the volume within the dimensions of the complex must be occupied by solvent. Preparations of the core of the complex are primarily composed of 60 dihydrolipoyl acetyltransferase (E2) subunits whose inner domains associate to form a pentagonal dodecahedron that is readily observed by electron microscopy (particle radius 10.7-11.3 nm). However, the bulk of E2's mass is present in an exterior multidomain structure. These mobile outer structures are very difficult to observe by standard electron microscopy techniques. Preparations of the core formed stable aggregates that were removed by gel filtration chromatography. QELS measurements gave an rH of 20.1 +/- 0.8 nm.(ABSTRACT TRUNCATED AT 250 WORDS)