A model for the structure of bovine parathormone derived by dark field electron microsocpy.

We have analyzed images of parathormone obtained by dark field electron microscopy in order to determine the three-dimensional structure of the molecule. The technique of autocorrelation was used to differentiate hormone particles from the background of noise in the electron micrographs. Our data suggest that parathormone is about 36 A in maximum dimension and is comprised of two interconnected domains of different mass that occur in a consistent orientation to each other. By means of the formulation of Chou and Fasman (Chou, P.Y., and Fasman, G.D. (1974) Biochemistry 13, 211-222), we predicted the secondary structure of the hormone and fitted this into the three-dimensional structure developed by microscopy. The resultant speculative model can explain certain physical and chemical properties of parathormone.