ADSORPTION OF PHAGE TO HOST CELL 147 



In Studying the adsorption of various phages to sintered-glass 

 filters, Puck, Garen, and Cline (1951) noted that cofactor-requir- 

 ing strains of phage T4 adsorb to glass in the presence but not 

 in the absence of tryptophan. A variant of T4 which does not 

 require cofactors for adsorption to cells adsorbs to glass in the 

 absence of tryptophan. This observation discouraged the view 

 that tryptophan might serve to activate an enzyme responsible 

 for adsorption. 



4. The Stepwise Nature of Adsorption 



Some experiments by Hershey, Kalmanson, and Bronfen- 

 brenner (1944) discussed above demonstrate that phage T2 can 

 adsorb to its host cell in salt-free broth, but that under these con- 

 ditions it fails to infect. On dilution in salt-free broth some of 

 the adsorbed phage elutes. These experiments demonstrate 

 that adsorption of phage to susceptible bacteria is not equivalent 

 to infection. A similar experiment was performed by Puck, 

 Garen, and Cline (1951) with phage T2. They also obtained 

 clear-cut evidence for the reversibihty of phage adsorption under 

 certain environmental conditions. 



Under other conditions, adsorption is irreversible and Garen 

 and Puck (1951) investigated the hypothesis that irreversible ad- 

 sorption is a two-step reaction passing through a reversible 

 phase. Several methods were devised for separating the steps, 

 mostly in experiments with phage Tl . One method depends on 

 effects of temperature. The rate of attachment of Tl to its host 

 cell was determined by centrifuging the undiluted adsorption- 

 mixture (so that elution would not occur) and assaying the super- 

 natant fluid for unadsorbed phage after various periods of ad- 

 sorption. Under these conditions, the first-order velocity con- 

 stants were 2.7 X 10~^ ml. per minute at 2° C. This result 

 showed that the rate of adsorption was indifferent to temperature 

 except for small effects that might be attributed to the change in 

 viscosity. This result was unexpected since Puck, Garen, and 

 Cline (1951) had previously reported a 40-fold increase in rate of 

 adsorption with a rise in temperature from to 37 ° C. How- 



