154 



PHOTOCONTROL OF GROWTH 



140 



120 



100 



O 



1^ 80 



5 60 



>- 



o 



< 



20 



40 80 120 160 200 240 



EXTRACT CONCENTRATION 



(M6 EQUIVFW. /ML REACTION MIXTURE) 



Fig. 5. The effect of cofactor concentration on the lAA oxidase activity 

 of etiolated pea epicotyl brei supplemented with IQ-^M MnCU. The 

 ordinate represents the change in optical density of an aliquot mixed with 

 Salkowski reagent for determination of residual indoleacetic acid. (K.U. 

 = Klett colorimeter units.) 



columns and on paper strips has been partially achieved by the use of 

 low concentrations of the lower alcohols, such as methyl, ethyl, iso- 

 propyl, and tertiary butyl. The Rf of the cofactor in 30% ^butanol is 

 0.7-0.8. With solvents such as benzene, methyl ethyl ketone, and 

 n-butanol, the active component remains at the origin. The active area 

 has thus far been invariably associated with a substance fluorescing 

 bright blue under ultraviolet. 



The yield and stability of the cofactor are both improved by prior 

 extraction of the buds with ethyl ether, the ether extract being dis- 

 carded. The residual material is then extracted with 80% ethanol 

 which yields a reasonably stable solution of cofactor. Addition of the 

 original ether extract lowers activity and decreases stability. 



Removal of the alcohol in vacuo from the final extract yields a 

 cloudy aqueous solution which, upon standing, produces a copious 

 precipitate. Both the precipitate and supernatant liquid are completely 

 inactive by themselves, but when they are recombined, complete ac- 



