THE PROTEINS OF MICRO-ORGANISMS 329 



By hydrolysis proteins can be split up into their 

 constituent amino -acids and those which go to make up 

 any particular protein identified, but as to the arrange- 

 ment of the amino-acids in the protein molecule we are at 

 present largely ignorant. As a result of the study of the 

 proj)ortions of various amino-acids in proteins Bergmann 

 concludes that the total number of amino-acid residues, 

 Nt, in any protein can be expressed by the equation 

 Nt=2" X 3"' where 7^ and m are positive whole numbers. 

 The experimental values suggest that Nt=2^ X 3'^ =288 

 or whole number multiples of it. Since the numbers of 

 any particular amino-acid, such as glycine or alanine or 

 tryptophane, in the protein can also be expressed as 

 Ni=2'*' X T' it seems plausible to regard the amino- 

 acids as being arranged in a regular repeating pattern 

 in the peptide chain, the pattern being characteristic 

 of the protein. Thus in silk fibroin, for which Nt = 

 2^ X 3*, half the amino-acid residues consist of glycine, 

 Ng=2* X 3* ; that is each glycine unit is separated 

 from the next by another amino-acid. : — 



— G — X — G — X — G — X — 



The number of alanine residues is found to be Na = 2^ x 3"^ 

 which means that every fourth residue is alanine : — 



— G — X — G — A — G — X — G — A — G — X — G — A — 



Tyrosine occurs in much smaller quantities, represented by 

 Nt=2^ X 3^, indicating that every sixteenth amino-acid 

 is tyrosine : — 



— G — A — G — X — G — A — G — X — G — A— G — X — G — 



— A — G — T — G — A — G — X — G — A — G— X — G — A — 



— G— X— G— A— G— T— G— 



8imih\rly for the other amino-acids which fit into thr^ii- 

 ])laces in the ])epti(lo chaiii. which cojistitutos silk fi])i'()iji. 



