THE INITIATION OF BACTERIOPHAGE INFECTION 229 



of an enzyme associated with the bacteriophage. The direct demonstration 

 of an enzyme in T2 phage was shown by Barrington and Kozloff (1954, 1956), 

 and confirmed by Koch and Weidel (1956). 



Under conditions where up to 15 phage particles are adsorbed, each 

 particle causes the liberation of the same amount of material. This implies 

 that the enzyme can break down only a hmited amount of substrate. It is of 

 some interest to note that the amount of cell waU nitrogen released by one 

 phage particle is about 5 X 10~^* mg., which is similar to the amount of 

 nitrogen in the phage DNA. 



The phage enzyme apparently is not acting upon the attachment site on 

 the ceD. Jesaitis and Goebel (1955) and Weidel and Kellenberger (1955) have 

 shown that the isolated attachment sites for T4 and T5 (Fig. 6) are not broken 

 down by interaction with a phage. Although the precise nature of the sub- 

 strate for the enzyme is not known, Weidel and Pringosigh (1957) have 

 shown that the cell wall material released by large excess of phage enzyme 

 comprises most of the structural units of the cell wall which give it its rigidity. 

 The enzyme apparently does not affect the cell membrane. 



Shortly after attachment of a phage particle, there is a temporary change 

 in cell permeability which allows some of the cell contents to leak out of the 

 ceU (Puck and Lee, 1954, 1955). Since 0.25 M Mg++ or Ca++ inhibits both 

 leakage (Puck and Lee, 1955) and the action of the phage enzyme on the cell 

 wall (Brown and Kozloff, 1957), the leakage probably is due to the action of 

 the phage enzyme on the outer cell wall. However, there is some confusion 

 about the relationship of the leakage due to the action of phage enzyme and 

 that due to the effects of other agents which also cause cell lysis (Tolmach, 

 1957). Any agent which interferes with the normal synthesis of the cell wall 

 components also leads to leakage and lysis by reactions unrelated to those 

 caused by the phage particle (Prestidge and Pardee, 1957). The fact that 

 leakage stops within 3-5 minutes after infection is probably a feature of 

 normal metabolism which maintains the cell wall integrity. 



Studies on the morphological localization of phage enzyme, which followed 

 closely after the work on the structure of the phage tail, revealed that the 

 intact phage is enzymatically inactive (Brown and Kozloff, 1957; Kozloff 

 and Lute, 1957a) and that the enzyme is exposed only after the tail is altered 

 by removal of the tail fibers. Although it would be desirable to isolate and 

 test the enzymatic activity of tail cores in order to be certain that they are 

 inactive (HgOg-treated phage have tail cores and are inactive), at the present 

 time it seems Ukely that the enzyme is located on the proximal tail protein. 

 It should be repeated in this connection that the proximal tail protein 

 apparently contracts upon interacting with the cell wall. The question can 

 be raised whether contraction is necessary to expose the enzyme and, 

 further, what is the relation between the phage enzyme and myosin-like 



