at4 receptor structurebinding relationship nterminalmodified angiotensin iv analogues the effect of structural changes in the nterminal amino acid of aiv with respect to at4 receptor binding was examined by competition with 125iaiv in bovine adrenal membranes analogues with modifications of the first residue alphaamino group possessed lower affinities than the primary aminecontaining parent compound peptides with a residue 1 alphacarbon in the d conformation exhibited poor affinity for the at4 receptor modifications of the residue 1 rgroup demonstrate that a straight chain aliphatic moiety containing four carbons is optimal for receptorligand binding as evidenced by the extremely high affinity of nle1aiv ki 359 051 pm replacement of the 12 peptide bond of aiv with the methylene bond isostere psi ch2nh increased the ki approximately fivefold indicating that the peptide bond may be replaced while maintaining relatively highaffinity receptor binding