 Lefkowitz made a remarkable contribution in the mid-1980s when he and his colleagues cloned the gene first for the β-adrenergic receptor, and then rapidly thereafter, for a total of 8 adrenergic receptors (receptors for adrenaline and noradrenaline).This led to the seminal discovery that all GPCRs (which include the β-adrenergic receptor) have a very similar molecular structure.The structure is defined by an amino acid sequence which weaves its way back and forth across the plasma membrane seven times.