Protein Clevage - (Nov/01/2015 )

Hello Everyone,

I am working on ATM (ataxia -telangiectasia mutant) protein, i found that the phosphorylated form of the protein presents two distinct bands, which i speculate that could be due to clevage by Caspase activation. What could be the other possible reasons for this

Thanks in advance and Appreciate the interesting suggestions. 

could be differential phosphorylation

or

some didn't phosphorylate (was one of the bands equal in migration with the unphosphorylated?)

which gel chemistry did you use to look at the effect(s) of phosphorylation?