The 50 kDa band is most likely the heavy chain. This appears when using human tissue or samples which may contain traces of blood. There are secondary antibodies such as Tru-Blot that can eliminate this heavy chain band.
This image shows human cervical carcinoma stained with ab46811 at 1/50 dilution.
This product has been referenced in:
Lopez R et al. Hyperglycemia enhances the proliferation of non-tumorigenic and malignant mammary epithelial cells through increased leptin/IGF1R signaling and activation of AKT/mTOR. PLoS One8:e79708 (2013).
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