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Insulin belongs to the disulfide-rich subclass of group 3 small ot/fi cytokines, which includes the insulin-like growth factors (IGF) 1 and 2, relaxin and bombyxin, and contains a conserved set of three disulfide bonds linking three short a-helices (Nicola, 1994). All insulin class cytokines/hormones bind to class II covalent tyrosine kinase receptors (Figure 1), and while the IGFs can also bind to the mannose-6-phosphate receptor, the biological relevance of this interaction is unclear at the present time. Insulin has a number of potent biological effects on metabolic processes including many aspects of glucose and lipid primary metabolism.

The established downstream mode of signal transduction for insulin is somewhat unusual. Engagement of the insulin receptor by insulin results in activation of tyrosine kinase activity in the receptor's (3-chain. This activity is able to autophosphorylate multiple tyrosine residues on the …