ASH IK AW A 81 



ments as a rapidly spreading fore peak [23] before the centrifuge is up to speed 

 (UTS). The growing cell components disappear as starvation progresses. 



The stability of microsome components isolated from log phase, stationary 

 phase, and starving cells and kept at 4° C or at room temperature in buffered 

 solvent was also studied. There was no detectable difference in stability between 

 particles isolated from log phase and those isolated from stationary phase. 

 Figure 3 shows the degradation of microsomes isolated from 48-hour stationary- 

 phase cells and suspended in phosphate buffer at 4° C. 



Since only the 80 S component is present in old stationary-phase cells and in 

 starving cells, the stability of this component isolated from proliferating, non- 

 proliferating, and starving cells, and dissolved in buffered solvent, was com- 

 pared. Figure ^a shows the sedimentation pattern at 0, 2, and 4 minutes after 

 UTS at 200,00% of the 80 S particles isolated from 24-hour stationary-phase 

 cells. The sedimentation pattern of this component from 72-hour nitrogen- 

 starved cells is similar, except for the broad, rapidly spreading, and sedimenting 

 fore peak. As shown in figure %, the 80 S component isolated from log-phase 

 and stationary-phase cells gave rise to the 60 S and 40 S component [24] when 

 kept at room temperature for 2 days. On the other hand, the 80 S component 

 isolated from cells nitrogen-starved for 72 hours became degraded by forming 

 rapidly sedimenting aggregates. See figures 4c and 5. 



DISCUSSION 



When starved cells are given utilizable nitrogen, the growth curve shows a 

 characteristic lag phase corresponding to the degree of starvation. During this 

 phase the 80 S component appears to be degraded and reconstituted. As shown 

 in figure 2, a decrease in the 80 S component is noted 1.5 hours after starved 

 cells are given utilizable nitrogen. Two hours after inoculation, the microsomal 

 concentration appears approximately equal to that of the inoculum cells. At 3 

 hours, new microsomal components appear in the cytoplasmic extract. The cells 

 are now entering the log growth phase, during which the microsome concen- 

 tration reaches a maximum. This condition is followed by a gradual quantita- 

 tive change in the microsomal components as the cells pass through the sta- 

 tionary phase. 



Chao and Schachman [8, 24] have shown that, in vitro, altering the ionic 

 environment of the solvent will dissociate or aggregate the 80 S component. It 

 would therefore be interesting to ascertain whether a similar mechanism is re- 

 sponsible for changes in the microsomal components in respiring cells. 



Since the 80 S particles from only starving cells of low viability are degraded 

 by forming rapidly sedimenting aggregates (figures 4c and 5), there appears 

 to be a correlation between call viability and the chemical state of this particle. 



Furthermore, if microsomes are involved in the synthesis of proteins and lipids 

 [5, 15, 16], the changes observed in the microsomal components with cell growth 

 could be a mechanism that controls their synthetic activities. 



