Abstract
The conformation of the molecules in ACTH 4-10 was determined as part of a study of the conformations of the biologically active N-terminal fragments of ACTH. ACTH 4-10 crystallizes in 2 different superstructures. The substructure considered in the present work is monoclinic, space group C2, a = 25.75 (1) .ANG., b = 27.78 (1) .ANG., c = 20.35 (1) .ANG., .beta. = 114.0 (1).degree., Z = 8 molecules ACTH 4-10 plus 22 weight percent solvent. The crystals contain antiparallel .beta.-sheets, the orientations of the side groups are not found, because of disorder. The present crystal structure and those of other linear oligopeptides emphasize that antiparallel .beta.-sheets are energetically favorable. It is very unlikely, however, that the ACTH 4-10 crystals contain the molecules in their biologically active form.

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