Regulates insulin-dependent IRS1 tyrosine phosphorylation in adipocytes by modulating the availability of IRS1 to IR tyrosine kinase. Its association with IRS1 is required for insulin-induced translocation of SLC2A4 to the cell membrane. Involved in TNF-induced impairment of insulin-dependent IRS1 tyrosine phosphorylation. Interacts with PRKG1 (PubMed:10671526). Interacts with IRS1 (PubMed:25586176). Predominantly expressed in testis. Expressed in the adipose tissue (at protein level) (PubMed:25586176). In the testis it is restricted to spermatocytes and early round spermatids. Also expressed in cardiac fibroblasts. Down-regulated by TNF in adipocytes (at protein level). Belongs to the GKAP1 family.