CHAPTER VI 
PROTEINS AND CARBOHYDRATES 
Classification of Proteins. Committees for the American Society of 
Biological Chemists and the American Physiological Society have made 
the following recommendations concerning the proteins: 
First. The word protezd should be abandoned. 
Seconp. The word protein should designate that group of sub- 
stances which consists, so far as at present is known, essentially of com- 
binations of the a-amino acids and their derivatives, ¢.g., a-amino acetic 
acid or glycocoll; a-amino propionic acid or alanin; phenyl-a-amino 
propionic acid or phenylalanin; guanidin-amino valerianic acid or 
arginin, etc., and are, therefore, essentially polypeptids. 
Turrp. That the following terms be used to designate the various 
groups of proteins: 
I. Simple Proteins. Protein substances which yield only a-amino 
acids or their derivatives on hydrolysis. 
Although no means are at present available whereby the chemical 
individuality of any protein can be established, a number of simple 
proteins have been isolated from animal and vegetable tissues which 
have been so well characterized by constance of ultimate composition 
and uniformity of physical properties that they may be treated as 
chemical individuals until further knowledge makes it possible to char- 
acterize them more definitely. 
The various groups of simple proteins may be designated as follows: 
(a) Albumins. Simple proteins soluble in pure water and coagulable 
by heat. 
(6) Globulins. Simple proteins insoluble in pure water but soluble 
in neutral solutions of salts of strong bases with strong acids. 
(c) Glutelins. Simple proteins insoluble in all neutral solvents but 
readily soluble in very dilute acids and alkalies. 
(d) Alcohol Soluble Proteins. Simple proteins soluble in relatively 
strong alcohol (70 to 80 per cent) but insoluble in water, absolute 
alcohol, and other neutral solvents. 
(e) Albuminoids. Simple proteins which possess essentially the 
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