12 

 inducible catabolic dehydroquinase takes DHQ that comes 

 directly from quinic acid (by a specific NAD* quinate 

 dehydrogenase) to dehydroshikimate which is converted to PCA 

 and on to carbon building blocks generated by the TCA cycle. 

 The dehydroquinase functional domain of the pentafunctional 

 arom protein of yeast and fungi channels DHQ formed from 

 DAHP to EPSP, thus bypassing PCA formation and avoiding 

 futile cycling (17, 21, 28) . Both a NADPH specific QDH (V. 

 I. Ossipov, personal communication) and a quinate 

 dehydratase (V.I. Ossipov, personal communication) have 

 recently been shown. The NAD"^ specific QDH from E. nidulans 

 also will utilize SHK (34) . These two systems offer some 

 interesting possibilities for overlapping metabolism in 

 plants. For example, it is conceivable that a QDT might 

 convert quinate to SHK for synthesis of aromatic amino acids 

 (Fig. 1-3) to be utilized as precursors for the synthesis of 

 lignin and other compounds. 



Multiple Species of Shikimate Dehydrogenase 

 Shikimate dehydrogenase has been a popular enzyme 



choice for a variety of isoenzyme studies and multiple 



activities have been described on many occasions. 



The bifunctional DQT/SDH protein (NADP* specific) was 



examined in dicots (50) . No evidence of a separate DQT or 



SDH has been determined, thus far. 



