Figure 5: Bioanalytical tests for the parameters of molecular and cellular function. Advantages (in green), disadvantages (in red) and “neutral” criteria (in black) are given for assaying insulin receptor protein kinase activity (recombinant insulin receptor, fluorescent substrate peptide with consensus phosphorylation site, ATP, 0.8% agarose gel, 120 V, 55 mA, 20 min, extraction and fluorometric quantification of phosphorylated fluorescent peptide) and lipid synthesis (insulin concentration-response curves with response at 2.5 ng/ml for each variant of the incorporation of [3H]glucose into lipids in rat adipocytes, extraction and radiometric quantification of radiolabeled lipids) on the basis of the criteria for target qualification as exemplified for some insulin variants (symbols see Figure 1). Some alternative methods are listed at the bottom. The molecular basis for the activation of the insulin receptor protein kinase and lipid synthesis by insulin in adipocytes involving phosphorylation of the insulin receptor substrate protein in the cytoplasm and activation of the glucose transporter at the plasma membrane is depicted on the right.