Simplified isolation and molecular composition of NADH dehydrogenase of the respiratory chain.

A simplified procedure for the isolation of NADH dehydrogenase from the inner membrane of ox heart mitochondria is presented which permits relatively rapid preparation of the enzyme in a more stable form than that afforded by published methods. The protein thus isolated displays more than eight different subunits in gel electrophoresis under denaturing conditions, three of which are also present in the "low-molecular-weight form' of the enzyme prepared under more drastic conditions. Complex I contains several subunits, mostly of low molecular weight, not seen in soluble purified NADH dehydrogenase. It is suggested that some of these may be 'binding peptides' necessary in linking NADH dehydrogenase to ubiquinone reduction, analogously to the role of small peptides in linking succinate dehydrogenase to ubiquinone. The dehydrogenase isolated by the rapid method contains equimolar amounts of non-haem iron and labile sulphur, but on further manipulation non-haem iron (but no labile sulphur) is lost, resulting in ratios of S/Fe in excess of unity, as previously reported for preparations isolated by longer procedures.