THE SURFACE OF VIRUSES 129 



One feature of this type of process is that, although specific 

 attractions to identical surface distributions are very great, 

 there is considerable attraction to any surface of opposite 

 charge. The fact that viruses will attach to glass filters and 

 other adsorl)ents has been known for some time. Delbrlick (1940) 

 found that reversible attachment of T-1 to a Jena glass filter 

 was possible. Shepard and Woodend (1951) showed that T-2 

 phage can be adsorbed on to glass powder and celite filter aids 

 and that the adsorption rapidly lessens above 10~^ molarity 

 concentration. Puck, Garen, and Cline also demonstrated such 

 nonspecific adsorption and, in addition, made the important 

 point that a tryptophane-requiring mutant of T-2 would only 

 attach to a glass filter in the presence of the needed concentra- 

 tion of tryptophane. The surface groupings in this case therefore 

 require tryptophane to be present before they are formed. 



Note that this electrostatic attraction is not temperature 

 dependent except that the viscosity of the medium exerts a drag 

 on the motion of the virus and this, being mainly water, changes 

 rather slowly with temperature. 



The second phase of attachment is described by Garen and 

 Puck (1951). It was found by them that a part of the virus 

 attachment to a bacterium is reversible. This reversible attach- 

 ment does not kill the bacterium, takes place predominantly 

 at low temperatures, and, in the presence of Zn+^ ion, is the only 

 kind of attachment. Reversibility was established by dilution 

 in excess NaCl, which carries the virus to the low attachment 

 point as seen in Fig. 5.1. The question arises as to the nature of 

 irreversible attachment, which at 37° C is over 90% of the total 

 attachment. In studying this, they found that it is strongly 

 temperature dependent, with a AH^ of 18,000 calories/mole; 

 that ultraviolet light applied to the bacterium inhibits it; and 

 that ions are necessary for it to take place. They conclude that 

 this second process is enzymatic in character. 



The whole picture is then as follows. Surface charges of like 

 configuration and charge exist on both bacterium and virus. 

 In the presence of ions, one or the other preferentially attracts 

 ions, so that matching opposite charges now exist, with conse- 



