[Protein-analysis] heterooligomer or homooligomer

[SL]

Hi,

 From gel filtration + western, my protein looks much bigger (~ 200 kD) 
than its monomer size (~60 kD). I am just wondering if there is a method 
I can detect if it's a protein complex (with other proteins), or just a 
oligomer of itself.

Any suggestions are welcome.

Thanks.

LS