PROTEINS 95 



very weak acids and alkalis but insoluble in neutral fluids, e.g., acid 

 metaprotein (acid albuminate), alkali metaprotein (alkali albuminate). 



(c) Coagulated Proteins. Insoluble products which result from 

 (i) the action of heat on their solutions, or (2) the action of alcohol on 

 the protein. 



2. SECONDARY PROTEIN DERIVATIVES 1 



Products of the further hydrolytic cleavage of the protein molecule. 



(a) Proteoses. Soluble in water, non-coagulable by heat, and 

 precipitated by saturating their solutions with ammonium or zinc 

 sulphate, 2 e.g., protoproteose, deuteroproteose. 



(b) Peptones. Soluble in water, non-coagulable by heat, but not 

 precipitated by saturating their solutions with ammonium sulphate, 3 

 e.g., antipeptone, amphopeptone. 



(c) Peptides. Definitely characterized combinations of two or more 

 amino acids, the carboxyl group of one being united with the amino 

 group of the other with the elimination of a molecule of water, 4 e.g., 

 dipeptides, tripeptides, tetrapeptides, pentapeptides. 



CLASSIFICATION OF PROTEINS ADOPTED BY THE CHEM- 

 ICAL AND PHYSIOLOGICAL SOCIETIES 

 OF ENGLAND 



I. SIMPLE PROTEINS 



1. Protamines, e.g., salmine, clupeine. 



2. Histones, e.g., globin, scombrone. 



3. Albumins, e.g., ovalbumin, serum albumin, vegetable albumins. 



4. Globulins, e.g., serum globulin, ovoglobulin, vegetable globulins. 



5. Glutelins, e.g., glutenin. 



6. Alcohol-soluble proteins, e.g., zein, gliadin. 



7. Scleroproteins, e.g., elastin, keratin. 



8. Phosphoproteins, e.g., casein, vitellin. 



II. CONJUGATED PROTEINS 



1. Glucoproteins, e.g., mucins, mucoids. 



2. Nucleoproteins, e.g., nucleo his tone, cytoglobulin. 



3. Chromoproteins, e.g., hemoglobin, hemocyanin. 



* The term secondary protein derivatives is used because the formation of the primary 

 derivatives usually precedes the formation of the secondary derivatives. 



2 As thus defined, this term does not strictly cover all the protein derivatives com- 

 monly called proteoses, e.g., heteroproteose and dysproteose. 



a In this group the kyrines may be included. For the present it is believed that it will 

 be helpful to retain this term as defined, reserving the expression peptide for the simpler 

 compounds of definite structure, such as dipeptides, etc. 



4 The peptones are undoubtedly peptides or mixtures of peptides, the latter term being 

 at present used to designate those of definite structure. 



