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11 Dec 2019

To study the kinetics of this enzyme, a graduate student measured the velocity of the reaction at a substrate concentration of 0.1 mM substrate. He found that after 1 mM competitive inhibitor was added, the initial rate decreased to 1/4 of the original rate. KM, the Michaelis constant, is 0.5 mM. What is the KI, the dissociation constant for the inhibitor binding to the enzyme? (Hint: in the presence of the competitive inhibitor, Vo= Vmax [S]/(1+[I]/KI) KM+ [S])

The answer is 0.28 mM, please give a detailed explanation

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Related questions

1. (3%) You measure the initial rate of an enzyme reaction as a function of substrate concentration in the presence and absence of an inhibitor. The following data are obtained: [S] V0 âInhibitor +Inhibitor 0.0001 33 17 0.0002 50 29 0.0005 71 50 0.001 83 67 0.002 91 80 0.005 96 91 0.01 98 95 0.02 99 98 0.05 100 99 0.1 100 100 0.2 100 100

a) What is the Vmax in the absence of inhibitor?

b) What is the Km in the absence of inhibitor?

c) When [S] = 0.0004, what will V0 be in the absence of inhibitor?

d) When [S] = 0.0004, what will V0 be in the presence of inhibitor?

e) What kind of inhibitor is it likely to be?

2. (2%) An enzyme is inhibited by two distinct competitive inhibitors, IA and IB. IA is shown to bind with a Ki of 13 Î¼M while IB binds with a Ki of 150 Î¼M.

a) Which is the more potent of the two inhibitors?

b) The natural substrate for the enzyme has a Km value of 0.1 mM. How does the substrate binding affinity compare to each of the two competitive inhibitors?

3. (2%) Assuming they have equal affinity for the enzyme, why would a noncompetitive inhibitor be a more effective drug than a competitive inhibitor?

An allosteric interaction between a ligand and a protein is one in which: 74. changes in Km are negligible, so Km can be treated as a constant. C. binding of a molecule to a binding site affects binding of additional molecules to the same site. binding of a molecule to a binding site affects binding properties of another site on the protein. binding of the ligand to the protein is covalent. multiple molecules of the same ligand can bind to the same binding site. A. D. VO Vmax. E. varying [S] has no effect on Vo. 78. The steady state assumption, as applied to B. enzyme kinetics, implies: Km = Ks. the enzyme is regulated the ES complex is formed and broken down at equivalent rates. the Km is equivalent to the cellular substrate concentration A. B. C. C. D. D. E. the mximum velocity occurs when two different ligands can bind to the same binding site. E. the enzyme is saturated. The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics: 79. 75. One of the enzymes involved in glycolysis aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: Substrate added vo COmol/min) (mmol/L) A. apoenzyme. B. coenzyme. C. holoenzyme. D. prosthetic group. E. substrate 0.8 217 325 488 647 76. 1,000 The role of an enzyme in an enzyme- catalyzed reaction is to: bind a transition state intermediate, such that it cannot be converted back to substrate. ensure that all of the substrate is converted to product ensure that the product is more stable than the substrate. increase the rate at which substrate is converted into product. make the free-energy change for the reaction more favorable. A. The Km for this enzyme is approximately: B. C. D. E. A. 1 mM B. 1,000 mM. C. 2 mM D. 4 mM E. 6 mM 80. In competitive inhibition, an inhibitor: binds at several different sites on an enzyme. binds covalently to the enzyme. binds only to the ES complex. binds reversibly at the active site. lowers the characteristic Vmax of the enzyme A. B. C. D. E. 77. The benefit of measuring the initial rate of a reaction VO is that at the beginning of a reaction: A. [ES] can be measured accurately. B. changes in [S] are negligible, so [S can be treated as a constant

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