Insulin receptor substrates (IRS) subtypes are responsible for several insulin related activities, such as glucose homeostasis, cell growth, cell transformation, apoptosis and insulin signal transduction. The balance between Ser/Thr phosphorylation of IRS has been demonstrated to be an important regulator of insulin signaling. IRS1 has also been shown to be constitutively activated in cancers such as breast cancer, Wilm’s tumors, and adrenal cortical carcinomas. Does not recognize IRS peptide NOT phosphorylated at Ser616 and will not recognize IRS peptide phosphorylated at Tyr183. Also does not react with riboflavin carrier protein which is known to have multiple phosphate groups.