126 



THE CELL AND PROTOPLASM 



that several of the viruses have been iso- 

 lated in an essentially pure form, and that 

 the biological activity is a specific property 

 of the respective nucleoproteins. There is 

 always the possibility that the virus ma- 

 terials may represent a unique situation 

 and that there is something which has not 

 been comprehended as yet. However, it 

 seems to me that the time has arrived when 

 it can be said that virus activity is a spe- 

 cific property of the nucleoproteins with es- 

 sentially the same degree of assurance as 

 when it is said that the properties of water 

 are those of the water molecule or that the 

 hormone properties of insulin belong to the 

 protein molecule known as insulin. On the 

 basis of information now available, there- 

 fore, it may be concluded, that the different 

 nucleoproteins represent the respective 

 viruses in essentially pure form. The chem- 

 ical makeup of these active materials thus 

 becomes of importance. Quantitative chem- 

 ical analyses of several of the viruses have 

 been completed and in general they contain 

 about 50 per cent carbon, 7.5 per cent hy- 

 drogen, and 16 per cent nitrogen, together 

 with a little sulfur and phosphorus. No 

 lipoid or fat has been demonstrated in the 

 smaller viruses or in the plant viruses, but 

 it has always been found in purified prepa- 

 rations of vaccine and chicken-tumor vi- 

 ruses. Although much of the lipoid is re- 

 movable, it has not been determined 

 whether all of the lipoid can be removed 

 without loss of virus activity. In the case 

 of the chicken-tumor agent, attempts to re- 

 move the final 5 per cent of the lipoid re- 

 sulted in inactivation. It is possible, there- 

 fore, that lipoid may represent an integral 

 component of these viruses. MacFarlane 

 and Salaman have reported that purified 

 vaccine virus shows phosphatase and cata- 

 lase activities but not dehydrogenase ac- 

 tivity, and they consider that the enzymatic 

 activities are specific properties of the 

 virus. No other purified virus preparation 

 has been reported to have such enzymatic 

 activity. Rischkov found purified tobacco- 

 mosaic virus to have none of the ordinary 

 enzymatic activities. 



In the immediate future it is unlikely 



that studies on the composition of most of 

 the viruses will consist of more than routine 

 quantitative elementary chemical analyses, 

 for at present most viruses are readily 

 available only in amounts measurable in 

 milligrams. However, there is no reason 

 why the makeup of at least one typical 

 virus, that of tobacco mosaic, should not 

 be studied in great detail, for it is possible 

 to obtain this virus nucleoprotein in 100-gm 

 lots without undue effort. Preliminary 

 studies have been completed, and to date 

 the virus material has yielded on hydrolysis 

 only amino acids and a nucleic acid of the 

 yeast nucleic acid type. The amino acids 

 that have been identified include arginine, 

 aspartic acid, cysteine, glutamic acid, 

 leucine, lysine, phenylalanine, proline, 

 serine, tyrosine, and tryptophane. Histi- 

 dine, alanine, and glycine are either absent 

 or occur in amounts that have not been 

 measurable as yet. Ross has found the 

 glutamic acid to be the naturally occurring 

 dextro-rotatory glutamic acid. This is of 

 interest because of the striking demonstra- 

 tion by Kogel and Erxleben of the occur- 

 rence in cancerous tissue of glutamic and 

 other amino acids having markedly lower 

 optical rotations, which indicates the pres- 

 ence of the unnatural isomers. In view of 

 the apparent dependence of insulin activity 

 upon the presence of the disulfide linkage 

 in the molecule, the distribution of sulfur 

 in the tobacco-mosaic virus preparation was 

 studied. Of the 0.24 per cent sulfur usu- 

 ally found, about 0.18 per cent occurs as 

 cysteine sulfur and 0.04 per cent or less as 

 sulfate sulfur. Although methionine de- 

 terminations frequently yield results as 

 high as 0.04 per cent methionine sulfur, the 

 results are always somewhat lower follow- 

 ing dialysis and it is doubtful if the ma- 

 terial actually contains methionine. 



Loring, in preliminary studies on the na- 

 ture of tobacco-mosaic virus nucleic acid, 

 demonstrated not only that the acid is a 

 true nucleic acid by the isolation of guan- 

 ine, adenine, cytosine, and uridylic acid 

 but also that the acid differs in certain 

 respects from all known nucleic acids. He 

 found the diffusion constant of virus nu- 



