Dtrate synthase

Let us consider Figure 5.3 again. Both pyruvate kinase and dtrate synthase (enzymes III and V) are inhibited by elevated ATP concentrations. During citric acid production ATP concentrations are likely to arise (ATP produced in glycolysis) and either of these enzymes could, if inhibited, slow down the process. In fact all of the evidence suggests that both enzymes are modified or controlled in some way such that they are insensitive to other cellular metabolites during citric add production. 

Figure 9.2 Summary of reactions of the Krebs cycle. The names of the enzymes are dtrate synthase, aconitase, isodtrate dehydrogenase (there are two enzymes, one ubTizes NAD as the cofactor, the other NADPT it is assumed that the NAD -specific enzyme is that involved in the cycle), oxoglutarate dehydrogenase, sucdnyl CoA synthetase, succinate dehydrogenase, fumarate hydratase, malate dehydrogenase.

A furtfier way in which metabolic control may be exerdsed is the artifidal deprivation of required ions and cofactors, for example aconitase must have ferrous ions for activity. Conversely, addition of toxic ions is possible, for example aconitase is inhibited cupric ions. Finally foe use of metabolic analogues is possible. If monofluoroacetate is added to cells then monofluorodtrate is produced by dtrate synthase and this compound inhibits the activity of aconitase. Great care has to be taken when using metabolic analogues, however, foey are often less than 100% spedfic and may have unexpected and unwanted serious side effects. 

Enzymes a) dtrate synthase b) aconitase c) isodtrate ctehydrogenase d) o-oxoglutarate dehydrogenase e) suodnyl CoA synthetase f) sucdnate dehydrogenase g) fumarase h) malate dehydrogenase i) nucleoside diphosphokinase. 

---