Extra band on western blot of Insulin Recetor beta subunit (C-19) antibody - (Jan/12/2012 )

The western blot was done for CHO, COS-7 and NIH3T3 cell lysates which were also treated with DFP ( a protease inhibitor) using the insulin receptor beta antibody (C-19, purchased from Santa Cruz). I obtained the required band at 95kDa confirming the presence of the insulin receptor beta subunit in these lysates. But, why do I see an extra band at around 60 kDa also? What could be the reason behind that?

Please help!

that (those) extra band(s) are most likely an artifact (previously identified to be keratins) caused by old reducing agent and dust.