74 



in similar fractions from the NADP* affinity column. 

 Therefore, when ADH was purified by the earlier mentioned 

 procedure an HA column step was included to completely 

 remove SDH activity. Purification of PAT followed the 

 previously demonstrated procedure with a purification of 

 about 250-fold. 



Discussion 

 The SP-I and SP-II proteins, well separated from each 

 other on the Celite 545 column, were each purified further 

 to about 1100- and 900-fold, respectively, by a series of 

 chromatographic steps. This complete separation was always 

 repeatable under similar conditions of the Celite 545 column 

 step (at least 12 times) . SDH and DQT activities coeluted 

 at an activity ratio of about 5 throughout the entire 

 purification regimen for both bifunctional proteins. These 

 proteins may be isoenzymes from different compartments 

 (chloroplast and cytosol) or they may be isoenzymes residing 

 in different locations within the chloroplast. This second 

 possibility was reported for two DAHP synthase isoenzymes 

 (DS-1 and DS-2) presumably located in chloroplasts of 

 Arabidopsis (2) . Further studies which may elucidate 

 differential properties of the two proteins and localization 

 studies should provide information with respect to possible 

 isoenzyme species and their location within the plant cell. 



