ANIMAL VIRUSES 493 



Emission spectra of purified vaccinia virus preparations have shown that 

 the only metal present in the virus is Cu (Hoagland et al., 1941a). The copper 

 could not be separated from the virus particle by repeated washings, ultra- 

 filtration, or electrodialysis. In contrast, copper ions added to the virus pre- 

 parations could very easily be removed again. The copper concentration 

 increased during the purification of the virus and was present in approxi- 

 mately the same concentration in all purified preparations. These findings 

 strongly suggest that copper is an intrinsic part of the virus. The presence of 

 copper was first noticed after observation of a relatively enormous uptake 

 of oxygen in the presence of cysteine. Further investigations show^ed that 

 the copper containing material did not correspond to any of the known 

 copper oxidases. 



It is not clear whether catalase, also found in virus preparations, is 

 essential to the infective particles. In contrast to FAD and the copper ions, 

 this enzyme can be so strongly bound from solutions that it cannot be 

 removed by extensive washings. The same is true for hydrolytic enzymes, 

 like phosphatase and lipase, which are also associated with the infective 

 particles (McFarlane and Salaman, 1938; Hoagland et al., 1942). There is 

 no question that one must be exceptionally critical concerning the presence 

 in virus preparations of enzymes that are normally present in the host 

 cells. Unfortunately, suitable methods to differentiate between true virus 

 components and adsorbed cell material of this sort are not available. 



The biotin found (Hoagland et al., 1940c), using microbiological methods, 

 seems to be a true component of the virus, since it is not adsorbed from 

 solution in appreciable amount (Hoagland et al., 1942), and because infective 

 particles release biotin during hydrolysis. 



The KP antigen amounts to about 50 % of the infective particle. It may 

 be extracted from the infective particles with the aid of dilute alkali. From 

 chemical studies, the NP antigen is found to be a nucleoprotein containing 

 some 6 % DNA (Smadel et al, 1942). 



The seroimmunological behavior of the infective particles suggests that at 

 least the antigen portion of this nucleoprotem is located on the surface of the 

 virus particle (see Smadel, 1952b). This finding is difficult to correlate with 

 degradation experiments controlled by electron microscopy. These studies 

 show that the DNA of the virus, which is to a large extent a fraction of 

 the NP antigen, is located in the interior of the particle. After the earlier 

 work of Dawson and McFarlane (1948), Peters and his co-workers (Peters 

 and Nasemann, 1953; Peters and Stoeckenius, 1954; Stoeckenius and Peters, 

 1955) made extensive studies, using this method. On the basis of these 

 investigations and of studies on ultrathin-sections Peters (1956) has 

 proposed the structure of vaccinia virus illustrated in Fig. 1. In the 

 interior of the particle is a structure (a), which appears dumbbeU-shaped 



