S. cerevisiae PDC was purified to near homogeneity
from baker's yeast by modification of a published procedure. Highly
purified E1 was obtained by resolution of PDC with 2 M NaCl at pH 7.3
followed by FPLC on a Superdex 200 column. The weight-average molecular
weight of the PDC was determined by light scattering measurement to be
~8 x 106. On the basis of the known molecular weight of the complex and
its component enzymes and the experimentally determined polypeptide chain
ratios of E2/BP/E3, we estimated that the subunit composition of the
S. cerevisiae PDC is ~24 E1 tetramers, 60 E2 monomers, 12 BP monomers,
and 8 E3 dimers. Sufficient E1 was added to a sample of the PDC
preparation to increase the molar ratio of E1/E2 core to 60:1.