262 The Structure of Protoplasin 



molecular patterns: extended (^-proteins, extended proteins of the 

 collagen type, folded proteins of the a-type, and folded proteins of 

 the supercontracted type. 



To this scheme of molecular protein types, Astbury^^ and others 

 had previously added one other important structural feature, that 

 of the grid, formed by side-chains joining one protein main-chain 

 to another. If the paper on which the diagram of such a protein 

 grid is printed is thrown into a series of folds parallel to the side 

 chains, the a- or contracted protein molecular pattern is obtained. 

 A parallel alignment of grids results in the formation of a three- 

 dimensional lattice, or crystal. 



It was a haphazardly assembled three-dimensional pattern, in a 

 general way similar to the symmetrical pattern postulated by Ast- 

 bury, which the earlier colloidal chemists had in mind when they 

 wrote of brush-heaps; these later became more orderly in design. 



Astbury-"^ states that the contraction of muscle is due to the 

 supercontraction of the oriented myosin, the protein which is the 

 principal structural component of muscle. Similar suggestions had 

 been made by Mark^- and Meyer.^^ And now we may carry the 

 concept directly to protoplasm and say that the contractihty of 

 protoplasm is due to the supercontraction of its principal structural 

 proteins through the folding of molecular fibers symmetrically 

 aligned and joined one to the other by side chains so as to form a 

 three-dimensional lattice. As this is a general conclusion of far- 

 reaching significance in biology, it may be restated as follows: Con- 

 tractility, wherever it occurs in animate nature, whether in the most 

 elementary form of protoplasm or in highly specialized tissue, is due 

 to the shortening of protein fibers by molecular folding. The energy 

 for this work is supplied by the oxidative processes of the cell. 



The physical basis of the mechanism of protoplasmic contrac- 

 tility has been set forth. The source of the energy is suggested. 

 There remains the interesting and rather speculative question, 

 whether the rhythm of protoplasmic movement lies in the chemical 

 reaction which supplies the energy, or in the mechanism where the 

 energy is used. If the energy supply is rhythmic, then there must 

 be a periodically reversible chemical reaction in protoplasm. A 

 number of autocyclic rhythmic reactions are known to occur in 

 protoplasm; the glycogen-lactic-acid cycle in muscle is one. A still 



20 



Fundamentals of Fiber Structure, London. 1933. 

 Proc. Roy. Soc. London, B 129, 307. 1940. 



