3-DIMENSIONAL STRUCTURE OF BOVINE NADH-UBIQUINONE OXIDOREDUCTASE (COMPLEX-I) AT 22 ANGSTROM IN ICE

NADH:ubiquinone oxidoreductase (complex I) is the first and largest co mplex in the electron transport chain of mitochondria. The bovine comp lex purified from cardiac muscle consists of at least 42 different sub units with a combined molecular mass of about 890 kDa. The three-dimen sional structure of the complex was determined at 22 Angstrom from sin gle particles embedded in vitrified ice using electron cryo-microscopy . The structure was calculated using a new program to align particles, to correct for the contrast transfer function of the microscope, and to carry out the three-dimensional reconstruction of the complex. The bovine complex has the overall L-shaped appearance found in earlier st udies of the closely related complex I from Neurospora crassa, but it differs by having a thin stalk region Linking the membrane-bound globu lar arm with the intrinsic membrane domain. Thus, the stalk which meas ures about 30 Angstrom in diameter is likely to contain part of the el ectron transfer pathway linking the NADH binding site in the globular arm with the ubiquinone binding site in the membrane domain. The globu lar domain of bovine complex I is significantly bigger than that of th e N. crassa enzyme, suggesting that the apparent additional subunit co mplexity of the bovine enzyme is associated with the globular part. (C ) 1998 Academic Press Limited.