Illustration of the US physician and biochemist Robert J Lefkowitz (born 1943). Lefkowitz was the first to demonstrate that cells had receptors for hormones and other substances on their surfaces and that they transduced external signals into cellular responses. He was initially working with receptors for adrenaline (adrenergic receptors), but realised that they shared a molecular structure with other membrane proteins. This family of receptors were named G-protein-coupled receptors (GPCRs). Understanding the structure and behaviour of these receptors allowed drugs to be targeted at them. Approximately half of all medications used today target GPCRs. Lefkowitz was awarded the 2012 Nobel Prize in Chemistry, along with Brian Kobilka, for his discoveries of the structure and behaviour of GCPRs.