Question

Research in cell biology and metabolism has progressed due to the discovery of molecules that artificially stimulate or inhibit glucagon/epinephrine and insulin signaling pathways. Let’s say you are working in a lab cataloging the effects of a library of small molecules on these pathways and have a “hit” on molecule 1stAVNGR. Preliminary data on molecule 1stAVNGR indicates that the cardiac isoform of PFK2/FBPase2 is doubly phosphorylated when this molecule is present at micromolar concentrations in cell cultures. Given this context answer the following questions.

a. Under these conditions what is the predicted degree of association between the regulatory subunits and the catalytic subunits of PKA?

b. Further investigation of molecule 1stAVNGR indicates elevated levels of cAMP within the cell despite the absence of epinephrine or glucagon. Hypothesize two possible explanations for this data.

c. When cell cultures are given both molecule 1stAVNGR and molecule RedSKLL (a G-protein inhibitor) cAMP levels remain high (again despite the absence of epinephrine or glucagon). Given this new information hypothesize a possible explanation for the data.

d. In consideration of the data presented in this problem what would be the expected effect of molecule 1stAVNGR on glycolytic flux in a culture of cardiac myocytes? Explain your reasoning?

e. Finally, if molecule 1stAVNGR were infused into a culture of hepatocytes what would be the expected effect on glycolytic flux in these cells? Explain your reasoning.

Answer 1

Answer:

(a). PFK (phosphofructokinase) is an enzyme which catalyzes the fructose-6-phosphate to fructose-1,6 bisphosphate.

The molecule 1stAVNGr can acts as activator protein kinase A (PKA). This molecule contains both regulatory subunit and catalytic subunit. The two subunits work together in response to the cell. To activate the catalytic subunit, the regulatory subunit must bind to the cyclic AMP, it leads to the initiation of signaling cascade mechanism.

(b). Epinephrine and glucagon are the two hormones, which convert ATP into cyclic AMP to stimulate the glycogenolysis pathway. Here. 1stAVNGr molecule acts as a receptor for joining adrenalin and glucagon hormones. It can cross the membrane and binds to the enzymes of cyclic AMP synthesizing enzymes. Finally, it leads to the absence or depletion of epinephrine and glucagon levels in the cell.

(c). When the cell cultures are given both molecule 1stAVNGr and molecule RedSKILL (a G-protein inhibitor) cyclic AMP levels remain high (again despite the absence of epinephrine or glucagon), this is because G-protein is a membrane protein which can inhibit or stimulate the adenylate cyclase and 1stAVNGr molecule inhibit the synthesis of enzymes responsible for the epinephrine and glucagon hormones.

(d). When the 1stANNGr molecule is supplemented into a culture of cardiac myocytes, there is phosphorylation of ser483 and ser466 on PFK-2. This leads to the formation of fructose2,6-bisphosphate, which will stimulate PFK-1 enzyme.

(e). If molecule 1stAVNGRwere infused into a culture of hepatocytes, prevention of glycolytic flux and glycolysis takes place. This is because in the liver the activity of phosphofructokinase enzyme decreases. The 1stAVNGr molecule phosphorylates the enzyme in the hepatocytes.