•100 RADIATION HIOLOGY 



have observed motile cell.s in irratliated suspensions eontaining no cells 

 capable of forming visible colonies, indicating that the energy-conversion 

 enzyme systems were still timet ional. Anderson (1948) has shown that 

 bacteriophage synthesis can occur in ultra xiolet-irradiated cells. 



The phosphorus uj)take and distribution were found to remain normal 

 in irradiated cells (Abelson and Roberts, 1948). Morse and Charter (1949) 

 have studied riboiuu-leic acid (RXA), DXA, and protein synthesis in 

 normal and irradiated cells of A', coli B. Normally, the UNA content per 

 cell increases five- to tenfold, and DXA and nitrogen two- to threefold 

 dining the lag phase. After multiplication commences, nucleic acid per 

 cell, especially RX^A, decreases. Doses of ultraviolet sufficient to reduce 

 survival to 3-5 per cent produce no delay in the synthesis of nucleic acid. 

 Synthesis of RXA is of normal magnitude, but syntheses of DX"A and 

 nitrogen are reduced. Doses sufficient to reduce the viable count to 1 per 

 cent interfere immediately with all syntheses. Relatively little material 

 is synthesized during the normal lag period, after which RXA synthesis 

 appears normal, whereas DX"A and nitrogen syntheses are reduced. 



Giese (1941) studied the respiration and luminescence of Achromohactcr 

 fischeri cells after exposure to ultraviolet. Doses, which just inhibited 

 division of most of the cells, permitted a normal respiration rate for 5 hr, 

 followed by a decline in rate. The length of the period of normal respira- 

 tion was an inverse function of dose, whereas the amount of the decline 

 was proportional to the dose. Very large exposures resulted in an almost 

 immediate large decline in respiration. Luminescence was intermediate 

 in radiation sensitivity between division inhibition and respiration 

 inhibition. 



A similar period of apparently normal respiration of X-irradiated K. 

 coli B/r cells followed by a decline was observed by Billen et al. (1953), 

 who further observed that the duration of the normal period was substrate 

 dependent, being longer on pyruvate and succinate than on glucose. 

 With the Texas strain of E. coli, however, an immediate inhibition of 

 respiration was observed on pyruvate. The inhibition of respiration was 

 more pronounced at 37° than at 2C°C. 



Brandt H al. (1951) found that ultraviolet radiation inhibited the 

 adajjtive formation of galactozymase in Saccharomyccs cerevisiae. Doses 

 which completely inhibited synthesis of the enzyme had little effect on 

 preformed enzyme. Exposure to 4850 r of X rays did not inhibit forma- 

 tion of galactozymase, even though division was inhibited in 90 per cent 

 of the irradiated cells. 



In similar studies, Billen and Lichstein (1952) observed that increasing 

 doses of X rays caused an increasing inhibition of the adaptive formation 

 of formic hydrogenlyase in E. coli. Doses of 60,000-90,000 r had no 

 measurable effect on preformed enzyme but completely inhibited the 

 adajitive synthesis of formic hydrogenlyase. Although the inhibition of 



