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Chapter 13: Problem 6

The guanylate cyclase that responds to NO A. is in the catalytic domain of a membrane receptor. B. is also activated when atrial natriuretic factor (ANF) binds to its receptor. C. increases activity because of a conformational change when NO binds to its heme. D. is a monomeric enzyme. E. is found only in smooth muscle cells.

Short Answer

Expert verified
Answer: The correct statement is "it increases activity because of a conformational change when NO binds to its heme."

Step by step solution

01

Understand Guanylate Cyclase Structure

Guanylate cyclase is an enzyme that catalyzes the conversion of guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP) and inorganic pyrophosphate (PPi). There are two types of guanylate cyclase, membrane-bound, and soluble guanylate cyclase. The specific guanylate cyclase catalyzing the response to NO is called soluble guanylate cyclase (sGC).
02

Analyze Activation Mechanisms of Guanylate Cyclase

Soluble guanylate cyclase is activated when NO binds to its heme prosthetic group. The binding of NO leads to a conformational change in the enzyme structure, resulting in increased enzyme activity. Activation of membrane-bound guanylate cyclase occurs through the binding of atrial natriuretic factor (ANF) or other natriuretic peptides to their receptors.
03

Assess the Localization of Soluble Guanylate Cyclase

The soluble guanylate cyclase enzyme that responds to NO is found in a variety of cell types, including smooth muscle cells, endothelial cells, neurons, and platelets.
04

Establish the Structure of Soluble Guanylate Cyclase Enzyme

Soluble guanylate cyclase is a heterodimeric protein enzyme composed of two subunits: α and β. The heterodimeric structure is necessary for the enzyme's function.
05

Find and Eliminate Incorrect Statements

A. The guanylate cyclase that responds to NO is soluble guanylate cyclase which is not a membrane receptor. B. Activating role of ANF is associated with membrane-bound guanylate cyclase, not soluble guanylate cyclase that responds to NO. D. The guanylate cyclase that responds to NO is a heterodimeric enzyme (composed of two subunits: α and β), not monomeric. E. Soluble guanylate cyclase is not only found in smooth muscle cells, but also in other cell types such as endothelial cells, neurons, and platelets. Now, we have eliminated the incorrect statements.
06

Identify the Correct Statement

C. The statement "increases activity because of a conformational change when NO binds to its heme" is correct. When NO binds to the heme group of soluble guanylate cyclase, it causes a conformational change in the enzyme structure, which activates it and increases its enzyme activity. Hence, the correct answer is C.

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Most popular questions from this chapter

Manic depression may be caused by overactiviry of certain central nervous system cells, perhaps caused by abnormally high levels of hormones or neurotransmitters which stimulate phospholipidbased signal transduction (c.g., from phosphatidylinositol [PI]). Lithium has been used for many years to treat manic depression. In the presence of \(\mathrm{Li}^{*}\), the PI system is slowed despite continued stimulation and cells become less sensitive to these stimuli. Li \(^{+}\) may have two functions, inhibition of the phosphatase that dephosphorylates inositol trisphosphate and direct interference with the function of G proteins. Which of the following statements concerning G proteins is correct? A. G proteins bind the appropriate hormone at the cell surface. B. GTP is bound to G protein in the resting state. C. \(\alpha\) -Subunit may be cither stimulatory or inhibitory because it has two forms. D. Adenylate cyclase can be activated only if \(\alpha\) - and \(\beta\) -subunits of \(G\) protein are associated with each other. E. Hydrolysis of GTP is necessary for G protein subunits to separate.

How does elevation of cyclic AMP in eukaryotic cells lead to altered transcription of certain genes?

The ErbB/HER family of receptor tyrosine kinase genes are linked to many different types of human cancers. Overexpression of any of these genes would lead to an increase in the various receptors. ErbB2 encodes the HER2 protcin. This receptor does not bind any known extracellular growth factor, but it does form dimers with other growth-factor-bound HER receptors. Even modest overexpression of HER2 can alter normal cell growth regulation. Ras protein is a critical regulator in cell proliferation, and its activity is enhanced by activated tyrosine kinase. Elements of its action include all of the following except A. formation of cyclic GMP. B. adaptor proteins binding to phosphorylated ryrosines on receptor tyrosine kinase. C. recruitment and stimulation of Ras-activating protein. D. exchange of GDP for GTP on the Ras protein. E. initiation of a cascade in which several kinases are activated sequentially by phosphorylation.

Growth hormone releasing hormone (GHRH) produced by the hypothalamus binds to its pituitary receptor and leads to the production of growth hormone (GH) because of increase in cyclic AMP. Certain pituitary tumors result in hypersecretion of GH because of a mutation that produces a \(G_{s}-\alpha\) protein with a greatly diminished GTPase activity. Low GTPase activity in the mutated protein results in consitutive activation of \(G_{s}\) and adenylate cyclase because A. GTP-bound \(\alpha\) -subunit does not reform the \(\alpha \beta \gamma\) trimer. B. GTP-bound G protein binds more strongly to the membrane receptor. C. GTP reacts directly with adenylate cyclase to activate it. D. the trimeric form of the G protein is stabilized. E. adenylate cyclase is phosphorylated more readily.

Manic depression may be caused by overactiviry of certain central nervous system cells, perhaps caused by abnormally high levels of hormones or neurotransmitters which stimulate phospholipidbased signal transduction (c.g., from phosphatidylinositol [PI]). Lithium has been used for many years to treat manic depression. In the presence of \(\mathrm{Li}^{*}\), the PI system is slowed despite continued stimulation and cells become less sensitive to these stimuli. Li \(^{+}\) may have two functions, inhibition of the phosphatase that dephosphorylates inositol trisphosphate and direct interference with the function of G proteins. The PI system begins with activation of phospholipase \(C,\) which initiates a sequence of events including all of the following except A. activation of \(\mathrm{IP}_{3}\) by action of a phosphatase. B. increase in intracellular \(\mathrm{Ca}^{2+}\) concentration. C. release of diacylglycerol (DAG) from a phospholipid. D. activation of protein kinase \(C\). E. phosphorylation of certain cytoplasmic proteins.
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