Question

1. Aconitase is an enzyme that displays moonlighting behavior dependent on cytosolic [iron]. When the concentration of iron is low, aconitase undergoes a shift towards mRNA binding activities. Please speculate as to the structural basis for this [iron]-dependent activity switch. What is the role and function of the iron-sulfur cluster in aconitase? What is the physiologic relevance of aconistase’s functional dependence on [iron]?

2. What is necessary in an enzyme’s active site in order for a symmetric molecule to react asymmetrically with the enzyme? Please provide an example of this phenomenon using an enzyme from the citric acid cycle.

3. Metabolic functions must occur with high efficiency to insure continued survival of the organism. Why is a process as complex as the citric acid cycle actually an economical way for cells to do their metabolic business? How does the citric acid cycle interact with other pathways that we have talked about in this class? Do such overlaps between the citric acid cycle and other pathways enhance or hinder overall metabolic efficiency?

Answer 1

Solution :- The Aconitase is a mitochondrial enzyme involved you catalyzing the conversion of citrate to socitrate in the citric acid cycle and also ay human RNA binding iron regulatory protein.. The ivono -sulfur cluster of a conitase directly reacts with an enzyme substrate. It has an active (Reusiu] 24 cluster, which can convert to an inactive {re 3sunt , from due to low iron. . Therefore in the absence of its labile ( Fe 4s4} cluster, if it ceases to be an enzyme that converts citrate and isocitrate and becomes an RNA binding protein which Searned with . . Sonth .

which is found in the cytosol of eukaryotic cells. Therefore, due to the interconversion, i, e. M-RNA binding and . conversion of citrate to isocitrate known as moonlighting effect 2. ANS: To catalyze a reaction, an enzyme coil grab on (binds to one a more reactant moecules. These molecules are the enzyme's substrates. In some reactions, one substrate is broken down into multiple products. In others, two substrates come together to create one larger molecule or to swap pieces. In fact, whatever type of brological reaction you can think of, there is probably an enzyme to speed. it up The part of the enzymes where the substrate binds is called the active site. Proteins are made of units. called amino acids, and in enzymes that are proteins. from the amino acids it is built out of The sci of amino acids found in te active site, ... along with theiv positions in 3D space, give the actre site a very specific size, shape, and chem I e shape, and chemical behaviour anned with

Thanks to these amino acids an enzyme's active site is uniquely suited to bind to a particular target the enzymes substrate or substrates -and help them undergo a chemical reaction. Example of this phenomenon using an enzyme Citrate synthascó It is an enzyme active in all examined cells, where it is most often responsible for catalyzing the first reaction of the citric acid cycle. (krebs cycle on the tncarbonylic acid (TCAJ cycle): The condensation of acetyl-CoA and onolocetes del to form citräte. Although in cukuryotes. it is a .. mitochondrial enzyme, and in fact is often used as a enzyme market for intact mitochondria, it is encocked bu nuclear DNA. The standard free energy change (AG") for the citrate synthase reaction is -31-5 kalmol. This negative free enery value means that citrate synthase is likely to function far. Form equilibrium under physiological eonditions, and is tous a rade determining enzyme in the air citric acid cycle N .
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