Question

In terms of the functioning of the beta-adrenergic pathway, give the rationale for the fact that adenalyl cyclase converts ATP to cAMP.

Answer 1

Answer-

According to the given question-

• cAMP or 3' , 5' - cyclic adenosine mono phosphate is work as secondary messenger and helps in regulation of several physiological function .
• It translates the signal from the extracellular stimulus into specific type of intracellular response. But the level of cAMP is depend upon its generation and breakdown or degradation.
• When an extracellular second messenger such as hormones, drug, neurotransmitter, chemokines binds with GPCR or G protein coupled receptor then adenyl cyclase or AC catalyzes the conversion of ATP into cAMP.
• cAMP is broken down or degraded with the help of phosphodiesterase into 5' - adenosine mono phosphate or AMP and this leads to termination of cAMP signal.Beta adrenergic receptor present in ventricular myocytes responsible for activation of adenyl cyclase which generates by catalyzing ATP to cAMP .
• now this cAMP activates PKA or protein kinases which are cAMP dependent. PKA responsible for phosphorylation of several proteins such as MyBP- C or myosin binding protein C, toponin I ot TnI.
• Catecholamines also activates Beta adrenergic receptor as well as cAMP / PKA signaling. So we can say that the specificity of cAMP signals for hormones is depend upon specific locations of several effectors of G protein coupled receptors, adenyl cyalase and cAMP as well as regulators which selectively activates different types of PKA and leads to phosphorylation of particular target due to specific types of stimulus.
• Phosphodiesterase which degrade cAMP and control their level depend upon the phosphorylation by PKA.
• e.g. When a Beta adrenergic receptor agonists such as isoproterenol or PEG1 or prostaglandins E1 showed different effect when there is same level of cAMP is present for both the receptor agonists. stimulation of Beta adrenergic receptor activated protein kinase A which activates phosphorylase kinase , troponin I as well as glycogen phosphorylase . while PEG1 increases level of cAMP and activates soluble protein kinase A but not causes any change in substrate of protein kinase A related to metabolism of glycogen..