1. You are studying the control of cAMP levels in brain slices. You have confirm
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Question
1. You are studying the control of cAMP levels in brain slices. You have confirmed that drugs such as isoproteronol that act through beta-adrenergic receptors cause a modest increase in cAMP as expected from G-protein mediated coupling between the receptor and adenylyl cyclase. You find a puzzling synergy, however, between isoproteronol and a number of pharmacological agents that be themselves have no effect of cAMP levels. What is the basis for this paradoxical augmentation of cAMP levels? A biochemist friend of yours has suggested a possible explanation: she has found in in-vitro experiments that beta-gamma subunits from inhibitory trimeric G proteins stimulate type II adenylyl cyclase, which is expressed in the brain. To test this idea in cells you plan to express the cDNAs encoding the component proteins in human kidney cells, which lack the receptors found in the brain. In this way you hope to reconstruct the effects you observed in the brain slices You transfect the kidney cells with various combinations of cDNAs encoding type II adenylyl cyclase, the dopamine receptor (which interacts with an inhibitory G protein), and a mutant (constitutively active) alpha-s subunit. You measure the levels of cAMP in the resulting cell lines in the presence or absence of quinprole (Which activates the dopamine receptor). You also measure the effects of pertussis toxin, which blocks the signal from Gi coupled receptors by modifying the alpha-i subunit in such a way that it can no longer bind GTP and dissociate from its beta-gamma subunit. Doparrine Receptor++ Adenylyl Cydae + Always active a-s Pertussis Tcxin A. (10 points) Explain the effects of pertussis toxin in your experiments. B. (10 points) What do you experiments indicate is required for maximal activation of type II adenylyl cyclase? Propose a molecular explanation for the augmented activation of type II adenylyl cyclase C. (10 points) Predict the effects of expressing the cDNA for transducin (an unrelated G protein alpha subunit in the GDHP form) which does not bind to adenylyl cyclase but does bind tightly to free beta-gamma subunitsExplanation / Answer
Ans- A pertussis toxin have inhibitory effects on the experiment as shown in the graph attached in the question. It reduce the cAMP levels to some extent when it is present along with other stimulators and receptors.
Ans-B according to experiment the trimeric G protein is required for maximal activation of type 2adenylyl cyclase. It will acts as a stimulator for the adenylyl cyclase and will enhance it's activity.trimeric protein will bind with adenylyl cyclase and produce a signal which allows the synthesis of cAMP.
Ans-C transducing is known for it's phosphorylation effect, it causes the break down of the cGMP. This protein transducin reduce the amount of cGMP and hyperpolarize the membrane potential. This is mainly found in rhodopsin of vertebrates.
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