April 3, 1908] 



SCIENCE 



555 



far as at present is known, essentially of com- 

 binations of a-amino acids and their deriva- 

 tives, e. g.j a-aminoacetic acid or glycoeoll; 

 a-amino propionic acid or alanin; plienyl- 

 a-amino propionic acid or phenylalanin ; 

 guanidin-amino valerianic acid or arginin; 

 etc., and are therefore essentially polypeptids. 



Third. — 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 de- 

 rivatives 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 constancy of ultimate com- 

 position and uniformity of physical prop- 

 erties that they may be treated as chem- 

 ical individuals until further knowledge 

 makes it possible to characterize 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) Olohulins. — 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-soluhle Proteins. — Simple pro- 

 teins soluble in relatively strong alcohol (70- 

 80 per cent.), but insoluble in water, absolute 

 alcohol, and other neutral solvents.* 



' The precipitation limits with ammonium sul- 

 phate should not be made a basis for distinguish- 

 ing the albumins from the globulins. 



' Such substances occur in abundance in the 

 seeds of cereals and doubtless represent a well- 

 defined natural group of simple proteins. 



•The sub-classes defined {a, h, o, d) are exem- 

 plified by proteins obtained from both plants and 

 animals. The use of appropriate prefixes will 

 suffice to indicate the origin of the compounds, 

 e. g., ovoglobulin, myoalbumin, etc. 



(e) Albuminoids. — Simple proteins which 

 possess essentially the same chemical structure 

 as the other proteins, but are characterized by 

 great insolubility in all neutral solvents." 



(f) Eistones. — Soluble in water and insol- 

 uble in very dilute ammonia and, in the ab- 

 sence of ammonium salts, insoluble even in 

 an excess of ammonia; yield precipitates with 

 solutions of other proteins and a coagulum 

 on heating which is easily soluble in very di- 

 lute acids. On hydrolysis they yield a large 

 number of amino acids, among which the basic 

 ones predominate. 



(g) Protamins. — Simpler polypeptids than 

 the proteins included in the preceding groups. 

 They are soluble in water, uneoagulable by 

 heat, have the property of precipitating aque- 

 ous solutions of other proteins, possess strong 

 basic properties and form stable salts with 

 strong mineral acids. They yield compara- 

 tively few amino acids, among which the basic 

 amino acids greatly predominate. 



II. Conjugated Proteins. — Substances which 

 contain the protein molecule united to some 

 other molecule or molecules otherwise than as 

 a salt. 



(a) Nucleoproteins. — Compounds of one or 

 more protein molecules with nucleic acid. 



(fc) Glycoproteins. — Compounds of the pro- 

 tein molecule with a substance or substances 

 containing a carbohydrate group other than 

 a nucleic acid. 



(c) Phosphoproteins. — Compounds of the 

 protein molecule with some, as yet undefined, 

 phosphorus containing substance other than 

 a nucleic acid or lecithins." 



(d) Hemoglobins. — Compounds of the pro- 

 tein molecule with hematin or some similar 

 substance. 



(e) Lecithoproteins. — Compounds of the 

 " These form the principal organic constituents 



of the skeletal structure of animals and also their 

 external covering and its appendages. This defini- 

 tion does not provide for gelatin, which is, how- 

 ever, an artificial derivative of collagen. 



' The accumulated chemical evidence distinctly 

 points to the propriety of classifying the phospho- 

 proteins as conjugated compounds, i. e., they are 

 possibly esters of some phosphoric acid or acids 

 and protein. 



