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8: Enzyme Inhibition

Students classify inhibition type (competitive, noncompetitive, uncompetitive, mixed) from changes in Km and Vmax in Michaelis-Menten data, and interpret inhibitor effects on Lineweaver-Burk plots.

LibreTexts reference: Unit 2, Chapter 3: Enzyme Inhibition LibreTexts

Cleavage Sites for Chymotrypsin Digestion of Peptides

Click to show Cleavage Sites for Chymotrypsin Digestion of Peptides example problem

Your professor provides your group with a peptide that will be the focus of your next enzymatic digestion experiment. Before performing the reaction, you are asked to predict where cleavage is most likely to occur under the planned conditions.
The peptide sequence is:
NH3+—Gly—Arg—Gly—Thr—Phe—Gln—Lys—COO–
You will be incubating the peptide with chymotrypsin in a buffered solution at physiological pH. Following digestion, you will analyze the products using mass spectrometry.
Which peptide bond will most likely to be cleaved during the incubation?

 

Determining Enzyme Inhibition Type from Metabolic Pathway Descriptions

Click to show Determining Enzyme Inhibition Type from Metabolic Pathway Descriptions example problem

A series of enzymes catalyze the reactions in the following metabolic pathway:

E1 E2 E3 E4 E5
D → E → F → G → H → I

Understanding the type of enzyme inhibition or activation is crucial for developing effective drugs and understanding metabolic regulation.

enzyme 1 converts substrate D into product E.

The end product I of this pathway binds to enzyme 1at a location far away from its active site.
This binding increases the activity of the enzyme.
Determine the type of enzyme inhibition or activation described:

 

Determining Inhibition Type from Enzyme Activity Data

Click to show Determining Inhibition Type from Enzyme Activity Data example problem

Michaelis-Menten Kinetics and Inhibition Type Determination
The table below presents data on enzyme activity measured as initial reaction velocities (V0) with and without the presence of an inhibitor at various substrate concentrations ([S]).

substrate
concentration, [S] 		initial reaction
velocity no inhibitor
V0 (–inh) 		initial reaction
velocity with inhibitor
V0 (+inh)
0.001  2.0  1.0 
0.002  3.9  2.0 
0.005  9.1  4.8 
0.010  16.7  9.1 
0.020  28.6  16.7 
0.050  50.0  33.4 
0.100  66.7  50.0 
0.200  80.0  66.7 
0.500  91.0  83.4 
1.000  95.3  91.0 
2.000  97.6  95.3 
5.000  99.1  98.1 
10.000  99.6  99.1 
20.000  99.8  99.6 
50.000  100.0  99.9 

Based on the data provided, determine the type of inhibition show by the inhibitor. Consider how the addition of the inhibitor affects the initial reaction velocities (V0) at various substrate concentrations ([S]).

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