DAVID L. CLAYBROOK 



239 



showed a peak absorption near 280 m/x, and the optical density 

 per milhgram of extract indicated a high percentage of protein. 

 All evidence, then, indicated that the active species were included 

 in the protein fraction. 



Fractionation of the active extract with ammonium sulfate (Ta- 

 ble 4) revealed that all activity was salted out, but was distributed 



Buds 



0.6 - 



0.4 - 



0.2 - 



0.0 



Incubation Time in Hours at 37°C 



Fig. 3. Effect of period of incubation with chymotrypsin on growth pro- 

 moting activity of non-dialyzable soluble extract. 



among several fractions. While supporting the conclusion that the 

 active components were proteins, this data showed that the activity 

 was apparently common to several classes of protein. 



The rate of inactivation of the extract by chymotrypsin is shown 

 in Figure 3. From this curve it would appear that intact protein 

 molecules, or relatively large fragments of them, are essential to 

 activitv in this extract. 



