Chapter IV —25— Chemical Constitue nts 



acid groups and the hydrolysis of these holoproteins results only 

 in amino acids and their derivatives. The heteroproteins are much 

 more complicated and are divided into nucleoproteins, phosphopro- 

 teins and glycoproteins. The heteroproteins give not only amino 

 acids by hydrolysis but other substances belonging to different 

 organic groups. 



The nucleoproteins may be considered as the combination of a 

 simple holoprotein and a nuclein, which is itself a combination of 

 holoprotein with a nucleic acid. Nucleic acids are esters of phos- 

 phoric acid containing, side by side with this acid, a sugar repre- 

 sented in plants either by a hexose or a pentose (ribose) as well 

 as organic bases of the purine series (guanine, hypoxanthine, 

 adenine) and of the pyrimidine series (cystosine). 



The phosphoproteins are proteins which, like the nucleopro- 

 teins, give on hydrolysis, amino acids and phosphorus-containing 

 substances other than nucleic acids. As for the glycoproteins, 

 they decompose by hydrolysis into proteins and sugar. The phos- 

 phoproteins and the glycoproteins are, moreover, very imperfectly 

 known. 



Holoproteins are always found in protoplasm but they seem to 

 play only a small part in the constitution of living matter. They 

 usually represent products of cellular metabolism and are chiefly 

 localized in the vacuoles where they constitute reserve products 

 (aleurone) . The greatest proportion of the constituents of living 

 matter seem to belong to the heteroproteins, among which the 

 nucleoproteins dominate. They do not seem to be exclusively local- 

 ized in the nucleus, contrary to an opinion often accepted, but they 

 are found also in the cytoplasm. In 1881, Reinke and Rodewald, 

 studying the chemical composition of the Plasmodium of Fuligo 

 septica, concluded that it is in large part made up of a phosphorus- 

 containing protein presumably formed by the union of a nuclein 

 and a protein. These results assigning to the cytoplasm a nucleo- 

 protein constitution have since been verified in material differing 

 greatly from the above. In 1892, Halliburton observed that the 

 nucleoprotein extracted by him from the kidney was in too great 

 quantities to have come from the nuclei alone and concluded cate- 

 gorically that this protein came above all from the cytoplasm. 

 Then in 1895, Halliburton isolated another nucleoprotein from 

 mammalian red blood corpuscles which do not have nuclei. These 

 analyses and many others published since, that of Lepeschkin 

 for example, actually indicate, it would seem, that the histochemical 

 proteins are nucleoproteins. It is admitted, however, that there 

 is a difference between the nucleoproteins of the cytoplasm and 

 those of the nucleus. In the former the nucleic acid is completely 

 saturated by the protein base while in the latter the saturation is 

 not complete and there is some uncombined nucleic acid. The 

 capacity of the nucleus to be stained with basic dyes is due, accord- 

 ing to this theory, to the uncombined nucleic acid which becomes 

 affixed to the basic dyes. So it would be explained that the nucleo- 



