Metabolite flow

Figure 9-2. An idealized cell in steady state. Note that metabolite flow is unidirectional.

Metabolite flow along a metabolic pathway is mainly determined by the activities of the enzymes involved (see p. 88). To regulate the pathway, it is suf cient to change the activity of the enzyme that catalyzes the slowest step in the reaction chain. Most metabolic pathways have key enzymes of this type on which the regulatory mechanisms operate. The activity of key enzymes is regulated at three independent levels ... 

C, for each enzyme in a pathway. This coefficient expresses the relative contribution of each enzyme to setting the rate at which metabolites flow through the pathway—that is, the flux, J. C can have any value from 0.0 (for an enzyme with no impact on the flux) to 1.0 (for an enzyme that wholly determines the flux). An enzyme can also have a negative flux control coefficient. In a branched pathway, an enzyme in one branch, by drawing intermediates away from the other branch, can have a negative impact on the flux through that other branch (Fig. 15-34). C is not a constant, and it is not... 

In rat heart mitochondria at pH 7.0 and 25 °C, the concentrations of reactants and products are oxaloacetate, 1 /am acetyl-CoA, 1 /am citrate, 220 /am and CoA, 65 /am. The standard free-energy change for the citrate synthase reaction is —32.2 kJ/mol. What is the direction of metabolite flow through the citrate synthase reaction in rat heart cells Explain. 

The individual pathways of carbohydrate metabolism in plants overlap extensively they share pools of common intermediates, including hexose phosphates, pentose phosphates, and triose phosphates. Transporters in the membranes of chloroplasts, mitochondria, amyloplasts, and peroxisomes mediate the movement of sugar phosphates between organelles. The direction of metabolite flow through the pools changes from day to night. 

Metabolite flow to tryptophan is controlled by inhibition of anthranilate synthase by tryptophan (see fig. 

In a third approach at localization of metabolites, flow cytometry was used to separate cell types of the sponge Dysidea herbacea (65). D. herbacea has... 

Broadly speaking, there are three basic patterns affecting the control of metabolite flow (Table I). The simplest is end-product inhibition in which the endproduct of a pathway is an... 

Enzymic Mechanisms Underlying Control of Metabolite Flow... 

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