H. Boumans et al., TOPOLOGICAL ORGANIZATION OF SUBUNIT-VII AND SUBUNIT-VIII IN THE UBIQUINOL-CYTOCHROME-C OXIDOREDUCTASE OF SACCHAROMYCES-CEREVISIAE, FEBS letters, 390(2), 1996, pp. 137-141
To determine the topology of subunit Vm of the yeast ubiquinol-cytochr
ome c oxidoreductase in the mitochondrial inner membrane, an epitope h
as been introduced in the N-terminal half of this protein, Previous to
pology studies had shown that at least the C-terminus faces the interm
embrane space [Hemrika and Berden (1990) fur. J, Biochem. 192, 761-765
]., Based on sensitivity of the protein to proteinase K digestion we n
ow suggest that the N-terminus of subunit VIII is similarly oriented,
implying that this subunit does not span the membrane, Despite this, h
owever, subunit VIII cannot be extracted from the membrane even after
treatment with 0.1 M Na2CO3 at pH 11.5, showing that the protein is in
tegrally embedded in the membrane, A similar behaviour was displayed b
y another low molecular weight protein of the complex, subunit VII, wh
ich faces the matrix side, A model for the topology of these subunits
in the membrane is discussed with respect to the structure of the comp
lex and their involvement in quinone binding.