L-Leu-L-Tyr, (I), C15H22N2O4, M(r) = 294.35, crystallizes from MeOH/5% dimethyl sulfoxide in the orthorhombic space group P2(1)2(1)2(1). a = 5.644 (1), b = 12.094 (3), c = 22.548 (4) A, V = 1539.0 (5) A3, Z = 4, Dx = 1.270 g cm-3, Cu K alpha, lambda = 1.54184 A, mu = 7.228 cm-1, F(000) = 632, T = 173 K, final R (on F) = 0.033 for 1347 observations with I > or = 2 sigma (I). (I) crystallizes as a zwitterion with the N-terminus protonated and the C-terminus ionized. The peptide backbone adopts a distorted trans antiparallel beta pleated-sheet conformation, with principal torsion angles psi 1 = 163.7 (2), omega 1 = 158.7 (2), phi 2 = -110.9 (3) and psi 2 = 141.4 (2)degrees. The leucyl residue is in the g-(tg-) conformation while the tyrosyl residue adopts the g- conformation, with the phenol ring twisted from the low-energy perpendicular position. Gly-D,L-Met.p-toluenesulfonate, (II), C7H15N2O3S+.C7H7O3S-, M(r) = 378.47, crystallizes from MeOH/EtOAc in the orthorhombic space group Pbca. a = 33.642 (4), b = 15.951 (1), c = 6.785 (1) A, V = 3641.0 (4) A3, Z = 8, Dx = 1.381 g cm-3, Cu K alpha, lambda = 1.54184 A, mu = 28.865 cm-1, F(000) = 1600, T = 223 K, final R (on F) = 0.055 for 1669 observations with I > or = 3 sigma (I). Gly-D,L-Met exists as a cation with the N- and C-termini protonated, the p-toluenesulfonate being the counterion.(ABSTRACT TRUNCATED AT 250 WORDS)