Answered: A plot of the reaction rate, V, vs. the…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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A plot of the reaction rate, \( V \), vs. the substrate concentration for an enzyme, alone and in the presence of either ATP and AMP, is shown below. Which of the following statements is TRUE regarding this enzyme?

(Graph description)
The graph is a plot with substrate concentration \([S]\) (moles/L) on the x-axis and reaction rate \( V \) (mmoles/L sec) on the y-axis. There are three curves represented on the graph:

1. The curve labeled "+AMP" is shown in blue, starting lower on the y-axis compared to the other curves and reaching the maximum rate (plateau) later as substrate concentration increases.
2. The curve labeled "+ATP" is shown in blue, starting higher on the y-axis compared to the "+AMP" curve and reaching the maximum rate quicker as substrate concentration increases.
3. The third curve, not specifically labeled, acts as a baseline and is positioned between the "+AMP" and "+ATP" curves.

These curves illustrate the effect of AMP and ATP on the enzyme's reaction rate with varying substrate concentrations.

Options:
A. A plot of 1/V vs. 1/[S] for this enzyme will yield a straight line
B. AMP inhibits this enzyme, but ATP activates it
C. This is an allosteric enzyme
D. All of the above
E. B and C

Transcribed Image Text:**Enzyme X Activity and pH Dependence** **Problem Statement:** The activity of Enzyme X is found to have the pH dependence as shown below. Based on the pH profile, which of the following proposals for the enzyme mechanism is consistent with this pH profile? (Amino acid pKa’s are shown below on the right) **Graph Description:** - The graph displays the relative reaction rate of Enzyme X on the y-axis, ranging from 0 to a maximum arbitrary unit. - The x-axis shows the pH range, from 2 to 10. - The curve peaks at pH around 6, indicating the highest enzyme activity. **Table: Typical pKₐ Values for Ionizable Amino Acid Side Chains in Proteins** | Amino Acid | Side chain pKₐ | |------------|----------------| | Cys | 8-9.5 | | Tyr | 9.5-10 | | Asp | 4-5 | | Glu | 4-5 | | Lys | ~10 | | Arg | ~12 | | His | 6-7 | **Multiple-Choice Options:** A. The active form of the enzyme has protonated Histidine and a deprotonated Glutamate. B. The active form of the enzyme has a deprotonated Lysine and protonated Histidine. C. The active form of the enzyme has a protonated Lysine and a deprotonated Histidine. D. The active form of the enzyme has a deprotonated Histidine and a protonated Aspartic acid. E. The active form of the enzyme has a deprotonated Aspartate and protonated Lysine. **Question Analysis:** The peak in enzyme activity at around pH 6-7 suggests that Histidine, with a pKa of 6-7, is involved. At this pH, Histidine is likely to be protonated. The pKa values suggest the likelihood of amino acid side chains being protonated or deprotonated at given pH levels.

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