- The spatial structure of methylamide N-acetyl-L-argine was studied taking into account the non-valent and electrostati interactions, the torsion energy, and the distorsion of valency angles. Calculation of the favourable conformations of the molecule was carried out with the use of all the combinations of angles phi, psi, chi1 divided by chi4 as an intital approximation. These correspond to the low energy forms of the main chain and to the minima of the torsion potentials of the side chain. Conformational possibilities of arginine and lysine were compared. The calculated stable conformation of N-acetyl-L-arginine-methylamide are compared with the geometry of arginine residues in the proteins with known structure.