14] TOBACCO MOSAIC VIRUS 259 



further purified by Dowex-2-XlO chromatography. It proved to contain only 

 two amino acids, having the composition ser,tyr. Both hydrazinolysis and 

 carboxypeptidase proved that the tyrosine was C-terminal which also is in 

 accord with known enzyme specificities. However, the status of the A^- 

 terminus of this simple peptide represented a considerable mystery. As stated, 

 its mode of isolation precluded the presence of a basic group. Furthermore, 

 the peptide did not give any ninhydrin color, nor a yellow DNP-derivative, 

 although it did give a colorless ether-soluble derivative which showed the 

 typical spectrum of 0-DNP tyrosine (Fig. 4). Previous suggestions that the 

 missing A^-terminus could be due to a loop peptide had to be abandoned 

 in view of the absence of aspartic or glutamic acid. It seemed that only the 

 presence of an acyl substituent on the amino group could account for the 

 observed properties of the acidic peptide. To search for such a component, 

 the peptide was hydrazinolyzed and the resultant mixture of hydrazides 

 (+ tyrosine) analysed by paper chromatography in search for any neutral 

 acyl-hydrazides. As shown on Table 1, the main component, as detected 

 with ammoniacal silver nitrate, showed Rf values, in two solvents, which 

 were identical with those of acetyl-hydrazide. 



Table 1 

 Rf VALUES OF SEVERAL HYDRAZIDES* 



A: Solvent: Pyridine -Aniline -Water (9 : 1 : 4, by vol.) 



Formic hydrazide 

 Acetic „ 

 Propionic „ 

 Serine „ 



Hydrazine 



B: Solvent: Collidine -Water (10 : 2, by vol.) 



Formic hydrazide 

 Acetic „ 



Propionic „ 

 Serine „ 



Hydrazide 



Decomposition product of 

 serine or its hydrazide 



Hydrazinolysate 

 of seryl-tyrosine 



* Detecting reagent: Ammoniacal silver nitrate reagent (0-1 n- 

 1 : 1 by vol.). 



-AgNOg, 0-5 N— NH4OH, 



