25 

 and 460 nm excitation) . Unless otherwise stated, a total 

 vol of 400 /xl contained substrates and 50 mM EPPS-KOH buffer 

 at pH 8.6. The rate is expressed as f luorometric units per 

 min (FU min-^ . Activities were calculated as nmol min"^ by 

 relating experimental values to a standard curve obtained 

 with authentic NADPH. Any background rate seen when 

 cofactor was present alone in reaction sample (only in some 

 crude extracts) was subtracted from the rate obtained from 

 reaction sample containing both substrates to give an 

 appropriate correction. A spectrophotometric assay was also 

 used occasionally by following the rate of formation of 



NAD(P)H at A340 nm- 



Aroaenate dehydrogenase . Arogenate dehydrogenase 

 activity was determined when . 5 mM AGN was added to the 

 reaction assay after . 5 mAT NADP* had been added or as 

 otherwise stated. When appropriate, NAD* was added as 

 cofactor to the reaction mix. 



Prephenate dehydrogenase . Prephenate dehydrogenase 

 activity was assayed with 0.5 mAf NADP* (or NAD*) and 1 . mAT 



PPA. 



Shikimate dehydrogenase . Shikimate dehydrogenase 

 activity was usually assayed in the reverse-of -physiological 

 direction with 1 . mM NADP* and 4 . mM SHK, unless otherwise 

 stated. When appropriate, NAD* was added to the reaction 

 sample. In the forward direction, SDH was assayed with 



