MOLECULAR MORPHOLOGY 53 



pattern in electron micrographs. The shafts of Paramecium trichocysts 

 show very regular periodic structure in the electron microscope, but 

 this object has not yet been studied with x-rays. In addition to the large 

 fiber-axis periodicities, the fibrous proteins may also show large lateral 

 separations, and these further assist the characterization of the protein. 

 The information on these large periods is summarized in Table I. 



TABLE I 



Large Repeating Periods in Fibrous Proteins 



Another approach to the problem is to make electron microscope and 

 x-ray studies of fibrous proteins in which reactive groups have been 

 altered chemically, as by deamination, deguanylation and so on. Such a 

 program is currently being undertaken at M.LT. on the protein collagen. 



Finally, a word must be said about the nucleoproteins. In Astbury's 

 study of mixtures of thymonucleic acid with the protamine, clupein, 

 the x-ray patterns were very similar to those of nucleic acid alone. The 

 only aspect which is stressed by Astbury is a fiber-axis period of 3.34 A 

 which is characteristic of nucleic acid and is supposed to indicate the 

 separation between nucleotide residues. Since this spacing is close to 

 3.5 A, the distance between amino acid residues in fully extended beta 

 proteins, Astbury supposes a salt linkage between protein side chains 

 and phosphoric acid residues of the nucleotides. 



Fluxional methods have shown that nucleic acid occurs as large 

 highly asymmetric particles of columnar shape. From polarization 

 optics it is known that in these columnar particles the nucleotide resi- 

 dues are oriented with long axes perpendicular to the axis of the col- 

 umns. The picture resembles stacks of coins. In each stack the coins are 

 bonded to each other near the periphery of the stack. Unfortunately, no 

 further detail can be furnished. 



