IRS1 and type 2 diabetes mellitus: However, we found diminished basal serine-632 IRS-1 phosphorylation in obese muscle, and insulin only mildly activated serine phosphorylation, compared to unstimulated obese, as opposed to previous studies showing the hyperphosphorylation of serine-632 IRS-1 in the muscle cells of type 2 diabetes [35,49,50].