PROTEINS. 09 



II. CONJUGATED PROTEINS. 



1. Glucoproteins, e. g., mucins, muco'ids. 



2. Nucleoproteins, e. g., nude o hist one, cy 'to globulin. 



3. Chromoproteins, e. g., hemoglobin, hcemocyanin. 



III. PRODUCTS OF PROTEIN HYDROLYSIS. 



1. Infraproteins, e. g., acid infraprotein (acid albuminate) , alkali 

 infraprotein (alkali albuminate) . 



2. Proteoses, e. g. } protoproteose, heteroproteose, deuteroproteose. 



3. Peptones, e. g., ampho peptone, antipeptone. 



4. Polypeptides, e. g., dipeptides, tripeptides, tetrapeptides. 



CONSIDERATIONS OF THE VARIOUS CLASSES 

 OF PROTEINS. 



SIMPLE PROTEINS. 



The simple proteins are true protein substances which, upon hy- 

 drolysis, yield only a-amino acids or their derivatives. "Although 

 no means are at present available whereby the chemical individual- 

 ity 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 constancy of ultimate composition 

 and uniformity of physical properties that they may be treated as 

 chemical individuals until further knowledge makes it possible to 

 characterize them more definitely." Under simple proteins we may 

 class, albumins, globulins, glutelins, prolamins, albuminoids, his- 

 tones and protamines. 



ALBUMINS. 



Albumins constitute the first class of simple proteins and may 

 be defined as simple proteins which are coagulable by heat and 

 soluble in pure (salt-free) water. Those of animal origin are not 

 precipitated upon saturating their neutral solutions at 30 C. with 

 sodium chloride or magnesium sulphate, but if a saturated solution 

 of this character be acidified with acetic acid the albumin precipi- 

 tates. All albumins of animal origin may be precipitated by sat- 

 urating their solutions with ammonium sulphate. 1 They may be 



1 In this connection, Osborne's observation that there are certain vegetable 

 albumins which are precipitated by saturating their solutions with sodium chlor- 

 ide or magnesium sulphate or by half-saturating with ammonium sulphate, is 

 of interest. 



