15 



Table 1-1. Molecular mass and Km values of DQT and SDH, 



Source 





Substrate 



Km imM) 



M/ 





Reference 



Sweet potato 



SHK 



1.300 



-- 





48 







NADP 



0.100 









Mung bean 



1 



DHQ 

 SHK 

 NADP 



0.130 

 0.220 

 0.025 



57,000 



(GE) 



49 



Mung bean 



2 



DHQ 

 SHK 

 NADP 



0.180 

 0.910 

 0.025 



57,000 



(GE) 



49 



Tomato 





SHK 



0.038 



73,000 



(GF) 



52 



Pea 





SHK 

 NADP 



0.690 

 0.013 



59,000 





61 



Corn 1 







-- 



55,000 



(GE) 



13 



Corn 2 







-- 



49,000 



(GE) 





Spinach 







— 



67,000 

 59,000 



(GF) 

 (GE) 



30 



Cucumber 





SHK 

 NADP 



0.060 

 0.010 



44,000 



(GF) 



53 



Radish 





SHK 

 NADP 



0.860 

 0.090 



60,000 



(GF) 



71 



Spinach 





SHK 



0.480 



44,000 



(GF) 



71 







NADP 



0.032 



49,000 



(GE) 





E. coli 







-- 



56,000 



(AA) 



28'' 



S. cerevisiae 





"■ ~ 



68,000 



(AA) 



77 



^Molecular mass estimated by gel filtration (GF) , by PAGE 

 (GE) or calculated from the deduced amino acid sequence 

 (AA) . 

 ''Molecular mass of monofunctional DQT and SDH were combined. 



sulfhydryl groups act as functional groups in the catalysis 

 of the enzyme and that partial reversal of inhibition is 

 accomplished by thiols (48, 53). Aromatic compounds, 

 metals, and salts have been studied with respect to effect 

 on DQT and SDH activities. Protocatechuic acid was found to 

 be a competitive inhibitor of SDH activity in tomato (52,) 

 and Cl' inhibited DQT activity competitively in pea (61) . 

 Ca^* stimulated SDH activity in Brassica rapa (71) . 



