THE PROTEINS 97 



convinced that it forms an integral part of these proteins. Both egg- 

 white and serum contain proteins belonging to the class of mucins, 

 ovomncoid and serum mucoid, each of which yields on acid hydrolysis 

 from 16 to 30 per cent, glucosamine. Since various observers have 

 obtained results varying from 1 to 16 per cent, glucosamine for crystal- 

 lised egg albumin, it seems possible that in every case the crystals 

 carried down with them some of the carbohydrate-rich mucoid, and 

 that the varying results were due to the different amounts of mucoid 

 present in the crystals. By our ordinary methods it is impossible to 

 prepare a specimen of either egg albumin or serum albumin which 

 is entirely free from this amino-derivative of carbohydrate. 



Connected with this group of proteins may be reckoned the diarnino- 

 trioxydodecoic acid already mentioned as occurring among the dis- 

 integration products of proteins. 



THE BUILDING UP OF THE PROTEIN MOLECULE 



By simple hydrolysis the protein molecule may be broken down 

 into a large number of amino- acids. Analyses of various proteins 

 show that these amino- acids are present in different proportions in the 

 individual proteins, so that in many cases a large number of identical 

 amino-acid groups must be present in the protein molecule with smaller 

 numbers of other groups. In endeavouring to form an idea of the 

 manner in which the amino-acids can be linked together into one gigantic 

 molecule, Hofmeister first put forward the idea that the linkage follows 

 the general formula : 



-CH 2 NH 00- 

 or -NH CH 2 CO NH- 



This theory of the constitution of proteins was based on the fact that 

 a similar grouping was known to occur in leucinimide, obtained by 

 the condensation of two molecules of leuciue, 



C 4 H 9 



/ OH \ 



NH CO 



CO NH 



and also by the fact that only a small proportion of the NH 2 groups 

 present in the separated amino-acids exist free in the protein molecule. 



7 



