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Chapter 12: Q27P (page 399)

Based on some preliminary measurements, you suspect that a sample of enzyme contains an irreversible enzyme inhibitor. You decide to dilute the sample 100-fold and remeasure the enzyme's activity. What would your results show if an irreversible inhibitor is present?

Short Answer

Expert verified

The affinity of the inhibitor for the enzyme is unaffected by the dilution factor.

Step by step solution

01

Enzyme inhibitors

Enzyme inhibitors stop enzymes from working.No other substrate can attach to the active site of the enzyme since the irreversible inhibitor binds to it irreversibly.

02

Results of reversible inhibitors is present

The substance is diluted 100 times to see if the sample contains an irreversible enzyme inhibitor. Even if the irreversible inhibitor is present, the enzyme solution activity is 100 times lower when diluting the sample. The enzyme inhibitor's affinity for the enzyme is more significant than the dilution factor. Thus, dilution won't affect if the enzyme inhibitor is irreversible.

Hence, the dilution factor does not affect the inhibitor's affinity for the enzyme.

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Most popular questions from this chapter

Explain why it is usually easier to calculate an enzyme’s reaction velocity from the rate of appearance of product rather than the rate of disappearance of a substrate.

MORE TO EXPLORE What kind of inhibitor is warfarin (shown in Fig. 12-20) and what enzyme does it inhibit? What is the physiological goal of warfarin therapy? Why do individuals vary in their response to a standard dose of warfarin? Why can a patient’s genotypic information help a physician choose an effective dose?

Sphingosine-1-phosphate (SIP) is important for cell survival. The synthesis of SIP from sphingosine and ATP is catalyzed by the enzyme sphingosine kinase. An understanding of the kinetics of the sphingosine kinase reaction may be important in the development of drugs to treat cancer. The velocity of the sphingosine kinase reaction was measured in the presence and absence of threo-sphingosine, a stereoisomer of sphingosine that inhibits the enzyme. The results are shown below.

[Sphingosine]

(𝛍M)

vₒ (mg min⁻¹)

(no inhibitor)

vₒ (mg min⁻¹)

(with threo-sphingosine)

2.5

32.3

8.5

3.5

40

11.5

5

50.8

14.6

10

72

25.4

20

87.7

43.9

50

115.4

70.8

Construct a Lineweaver-Burk plot to answer the following questions:

(a) What are the apparent KM and Vmax values in the presence and absence of the inhibitor?

(b) What kind of an inhibitor is threo-sphingosine? Explain.

Is it necessary for measurements of reaction velocity to be expressed in units of concentration per time (M s⁻¹, for example) to calculate an enzyme's KM?

For an enzyme-catalyzed reaction, the presence of 5 nM of a reversible inhibitor yields a Vmax value that is 80% of the value in the absenceof the inhibitor. The KM value is unchanged. (a) What type of inhibition is likely occurring? (b) What proportion of the enzyme molecules have bound inhibitor? (c) Calculate the inhibition constant.
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