Molecular basis of insulin receptor function.

Insulin regulates a wide spectrum of metabolic processes in a variety of tissues. In addition, insulin is a potent growth factor, promoting normal cell growth and division in cultured cells, though the physiological importance of such actions in man is less certain. Some of the effects of insulin are very rapid and apparent within seconds, for example those on transport processes and the activity of regulatory enzymes. Other effects, such as those on enzyme concentrations and cell growth, may be manifest only over a period of many minutes or even hours. Such differences in time dependence may be more a reflection of the nature of the processes themselves than an indication of different signalling mechanisms. However, it is still unclear whether the regulation of diverse metabolic processes by insulin involves just one or multiple distinct primary intracellular signals. We will review here what is at present known about the structure and activity of the receptor, and current ideas on signalling mechanisms.