 Alpha sheets have also been observed in X-ray crystallography structures of designed peptides.When Pauling and Corey first proposed the alpha sheet, they suggested that it agreed well with fiber diffraction results from beta-keratin fibers.However, since the alpha sheet did not appear to be energetically favorable, they argued that beta sheets would occur more commonly among normal proteins, and subsequent demonstration that beta-keratin is made of beta sheets consigned the alpha sheet proposal to obscurity.