CIII'MlSriy'Y OF I'h'oTKIXS ' 21 



Globulins also oocur in nil cells, hut in small amounts in most animal ceils 

 except llie muscles, whose cliief proteins helonp; to tliis or a closely related Kroup. 

 Tiie globulins are quite similar to the albumins, so that there is really no sliarp line 

 between the two j!;roups. Their insolubility in water separates them from albu- 

 mins, and their solubility in dilute lunitral salt solutions from the more complex 

 proteins. An important feature of tli(> f^loljulins is the low temperature at which 

 they coagulate — some so low that IIallil)urton' believes it possible that they may 

 be coagulated within the cells during high fevers. 



Hammarsten has long maintained that simple proteins form a relatively in- 

 significant part of the cytoplasm, in opjiosition tf) the once-prevalent view that 

 the nucleo-proteins were limited to tlie nucleus, and that the cytoplasm was chiefly 

 albumin and globulin. 'Plie general trend of opinion as influenced by the result.s 

 of researches has been favorable to his contentions, and we shall jjrobably not be 

 far wTong in accepting his statement that — "The chief ma.ss of the protein sub- 

 stances of the cells does not consist of proteins in tlie ordinary sen.se, but consists 

 of more complex phospliorized l^odies, and that the globulins and albumins are 

 to be considered as nutritive materials for the cells or as destructive products in 

 the chemical transformation of the protoplasm."^ 



Nucleo-proteins are considered to be the most important constituents of the 

 cell, botli in quantity and in relation to cell activity. In structure the nucleo- 

 proteins are very complex, as indicated by the difTerent products yielded on hydro- 

 lytic cleavage of the molecule. Furthermore, there are many varieties, depending 

 both upon the nature and proportions of the component parts. They may be 

 described as consisting of two primary constituents — (1) nucleic acid and (2) a 

 protein body, in chemical combination with each other like a salt. The term 

 itiicleic acid covers a large group of substances, which are characterized, on the 

 one hand, by their frequent occurrence bound with proteins, and, on the other 

 hand, by their yielding phosphoric acid and purine bases, pyrimidines and pentoses 

 or hexoses on cleavage. Diagranimatically the manner of cleavage of the nucleo- 

 proteins may be indicated as follows: * 



Nucleo-protein 



. /\ 

 nuclein^ protein 



nucleic acid protein 



phosphoric acid purine bases, pyrimidines and carbohydrates. 



In the cell the nucleo-proteins probably exist partly as solid structures, c. (j., 

 the chromatin framework of the nucleus, and partly dissolved in the plasma. An 

 interesting phenomenon is the alteration in the chromatin nucleo-proteins during 

 cell division, when they seem to lose part of the combined protein and approach 

 more. nearly pure nucleic acid — just as inorganic salts occur with the acids and 

 bases saturating each other more or less incompletely, e. g., mono-, di-, and tri- 

 basic phosphates. In this we have a chemical explanation of the intensity of the 

 staining of dividing nuclei by basic dyes." 



Phosphoproteins resemble nucleo-proteins to the extent that they also yield 

 phosphoric acid, and are somewhat similar in solubility and digestibility. They 

 are essentially different, however, in that they do not yield nucleic acid or purine 

 bases on cleavage. Probably members of this group are also constant components 

 of cells. 



Glycoproteins (or gluco-prnl(in>i) and phof^pho-c/lycnproteins are also believed to 

 occur frequently or constantly in protoplasm. They are compounds of proteins 

 with a sugar or sugar-like group, which probably usually contains nitrogen, thus 

 differing from the ordinary hexoses and pentoses. 



' Halliburton and jNIott, Archives of Neurology. 1903 (2), 727; also .see Halli- 

 burton's "Chemistry of Muscle and Nerve." 



'See Kossel, Munch, med. Woch.. 1911 (58), 65. 



* Probably nuclein should be considered as merely one variety of nudeoprotcin, 

 with less protein than the other varieties. 



' The chemistry of the nucleo-proteins is discussed in the chapter on Trie Acid 

 Metabolism and Gout, Chap, xxiii. 



