What non-SDS buffer can I use to isolate protein from mammalian cells? The protein is intended for testing electron transport chain complexes.
Short answer - you will need to use a nonionic detergent. These will dissolve lipid membranes but leave most protein complexes intact, and many proteins in active form.
However there are many of these available and finding the right one for a particular job is a black art.
The usual approach is to start off with something widely-used and not too expensive like Triton X-100. Detergents with glycoside head groups are also widely-used but tend towards the expensive.