Question

Epinephrine signaling , like that of insulin, is a multi-step pathway with several amplification steps. Identify each of the steps below as either allosteric activation or enzymatic.

Abbreviations: Epi (epinephrine),  β₂AR (β₂ adrenergic receptor), R₂C₂ (subunit composition of protein kinase A where R is the regulatory subunit and C is the catalytic subunit), PDE (cyclic AMP phosphodiesterase), PPase (phosphoprotein phosphatase).

Allosteric Epi+B2AR --> Epi-B2AR* hormone-receptor binding Allosteric Epi-B2AR* + GDP-Gsaßy + GTP --> Epi-B2AR*-GTP-Gsa + GBy + GDP GDP-GTP exchange Enzymatic |Epi-B2AR -GTP-Gsa + AC --> Epi-B2AR* + GTP-GSQ-AC* G-coupled AC activation Allosteric GTP-GSQ-AC* + ATP --> GTP-GSQ-AC* + cyclic AMP + PP cyclic AMP synthesis Enzymatic 4 cyclic AMP +R2C2-->(4 cyclic AMP)-R2 + 2C* PKA (R2C2) activation Enzymatic (* + protein + ATP --> (* + Phosphoprotein + ADP Protein phosphorylation The epinephrine signaling cascade terminates in several ways. Determine if each step is allosteric or enzymatic. Allosteric Epi-B2AR* --> Epi +B2AR hormone-receptor dissociation Enzymatic GTP-Gsq-AC* + GBy --> GDP-GsaBy + AC + Pi GTP hydrolysis Enzymatic CAMP + PDE --> AMP + PDE CAMP hydrolysis Enzymatic Phosphoprotein + PPase --> protein + Pi + PPase Protein dephosphorylation

One of these is wrong but I don't know which one you can only choose enzymatic or allosteric as the answer choice.

Answer 1

ANSWER:-

* Epinephrine signaling occurs when the hormone binds to an epinephrine receptor on the cell surface. The hormone triggers the receptor to change shape. converting the receptor to its active form. it is an allosteric activation as the binding of the epinephrine molecule causes conformation change in the receptor.

* The activated receptor triggers a cascade of events within the cell, beginning with the activation of a G protein. The G protein binds to the activated receptor, releases GDP, and takes up a molecule of GTP. it is an allosteric activation receptor causes conformation change in the G protein.

* Activated, adenylyl cyclase converts a large number of ATP molecules into signaling molecules, called cyclic AMP (cAMP).

The synthesis of cAMP by adenylate cyclase is an enzymatic step as the enzyme cleaves the ATP to produce cAMP.

* The cAMP molecules produced by adenylyl cyclase continue the signaling cascade by binding to a type of enzyme called protein kinase A. This binding triggers protein kinase A to separate into subunits, two of which are catalytically active.

it is allosteric activation as the binding of cAMP causes activation of the enzyme.

* The activated protein kinase A subunits perform chemical reactions in which type add phosphate groups to another type of enzyme, called phosphorylase kinase. The addition of the phosphate groups activates.

it is enzymatic step in which protein kinase A adds phosphate group to the enzyme phosphorylase kinase and activates it.

Termination of epinephrine signalling:

* After the G protein dissociates from the receptor, the receptor can get dissociated from the hormone, inactivationg it by changing the conformation of the receptor.

it is allosteric as the dissociation of the hormine causes the conformation change in the receptor.

* G protein can be inactivated by the hydrolysis of the bound GTP by the enzymatic acivity of the G protein, rendering the G protein inactive.

* cyclic AMP is inactivated by its enzymatic hydrolysis by the enzyme cyclic AMP phosphodiesterase.

* phosphoprotein is inactivated by the enzymatic clevage of the phosphate group by the enzyme phosphoprotein phosphatase.

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