step is not catalytic

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
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The epinephrine-mediated “amplification
cascade” of Figure 24.14 has six steps, all of which are catalytic
with one exception. This cascade leads to the activation of glycogen
phosphorylase. This enzyme acts in turn on glycogen to yield
glucose-1-phosphate (G-1-P).
(a) Which step is not catalytic?
(b) If each catalytic step had a turnover (molecules of substrate
acted on per molecule of enzyme) of 10, how many molecules
of G-1-P would result from one molecule of epinephrine?
(c) What is the biochemical advantage of such a cascade?
(d) How is the amplification cascade of this question
reversed?

 

Hormone
Receptor
- Adenylate cyclase
CAMP
GBGY
PP
RR
RR
АТР
Inactive
CAMP +
АТР
enzyme
GTP
GDP + P
Figure 24.14 The activation of adenylate cyclase by the binding of hormone
to the receptor and the mode of action of CAMP. The binding of hormone to the
receptor leads to the production of CAMP from ATP, catalyzed by adenylate cyclase;
this reaction is mediated by a G protein. Once CAMP is formed, it stimulates a protein
kinase by binding to the regulatory subunits, shown as R. The active catalytic subunits,
shown as C, are released and catalyze the phosphorylation of a target enzyme. The
target enzyme elicits the response of the cell to the hormonal signal. This scheme
applies in situations in which the phosphorylation activates the target enzyme.
Active
ADP
phosphorylated
enzyme
Cellular
response
Transcribed Image Text:Hormone Receptor - Adenylate cyclase CAMP GBGY PP RR RR АТР Inactive CAMP + АТР enzyme GTP GDP + P Figure 24.14 The activation of adenylate cyclase by the binding of hormone to the receptor and the mode of action of CAMP. The binding of hormone to the receptor leads to the production of CAMP from ATP, catalyzed by adenylate cyclase; this reaction is mediated by a G protein. Once CAMP is formed, it stimulates a protein kinase by binding to the regulatory subunits, shown as R. The active catalytic subunits, shown as C, are released and catalyze the phosphorylation of a target enzyme. The target enzyme elicits the response of the cell to the hormonal signal. This scheme applies in situations in which the phosphorylation activates the target enzyme. Active ADP phosphorylated enzyme Cellular response
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