The insuliri receptor is a transmembrane glycoproíeiri found in íhc plasma memhrane of many cell types. The initial step in insulin action is the hiriding of insulin to the cxtraccllular 01 subunit of thc insulin receptor (FIG. 1). Thc transmembrane and cytoplasmic f3 subunit is a tyrosine-specific protein kinase that is activatcd after insuliri binding and undergoes autophosphorylation. Subçequently, thc activatcd insulin receptor kinase phosphorylaies inlracellular substrates, which ultirnakly leads to the metabolic effects of the hormone.(For recent reviews see refs. 1 and 2.) The exact mechanism of transmembrane transduction of lhe signal from the CY to the p subunit is still largely unknown. Current evidence postulates thc existcnce of conformational changes in the a subunit upon binding of insulin, which are propagated to the f3 subunit through dimerizationioligomeriration of adjacent receptor molec~ les.~ It is then appropriatc to hypothesize that membrane lipids have a role in íhis transmembrane signaling.

Membrane lipid composition is known to affcct a number of cellular functions, such as carrier-mediated traiisports, membrane-bound enzynies, endocytotic processes: and cell gro~ th.~,~ The prcsent paper reviews currcnt experimental evidence for a modulatory role of membrane lipids in insulin receptor functions and discusses its possible importancc and mechanisms.