150 BACTERIOPHAGES 



that ko must have a low temperature coefficient, as might be ex- 

 pected for the rupture of ionic bonds. Garen and Puck (1951) 

 have reported evidence suggesting that /..-j may be an cnzymically 

 catalyzed reaction. Garen (1954) made a detailed study of the 

 reversible interaction between Tl and B/1, showing that the 

 rate of primary attachment of Tl to B and to B/1 is about the 

 same. 



This relatively simple conception of a two-step mechanism of 

 adsorption has been widely accepted and seems to be the most 

 reasonable explanation for the kinetics of adsorption of phages 

 Tl, T2, and T4 to their host cells. Tolmach (1957) thoroughly 

 reviewed the evidence for this view. Hershey (1957), however, 

 pointed out that the experimental evidence leaves much to be de- 

 sired, notably because no test has been made of the postulate that 

 the transition from reversible to irreversible attachment is pos- 

 sible and rapid. 



5. Chemical Nature of Receptor Sites 



There have been two principal approaches to the problem of 

 the chemical nature of the bacterial receptor sites for phage ad- 

 sorption. One approach involves a studv of the kinetics of 

 phage adsorption to bacterial cells treated with various agents 

 which might alter the cell surface. The second approach in- 

 volves a study of the chemical properties of the receptor sub- 

 stances after their isolation from the bacterial cells. 



The dominant role of salt concentration in the adsorption 

 process led Puck, Garen, and Cline (1951) to postulate that the 

 primary attachment of phage particle to host cell is by electro- 

 static bonds. The chemical nature of the charged groups in- 

 volved in adsorption was studied by Tolmach and Puck (1952) 

 and Puck and Tolmach (1954). They used phage labeled with 

 P'^- and studied the distribution of radioactivitv between super- 

 natant and sediment in centrifuged samples of adsorption mix- 

 tures. This technique permits the study of adsorption under 

 environmental conditions which would destroy the viability of 

 phage or host cell. The effect of pH was studied over the range 



