Question

Describe the pathway involved in the degradation of one triacylglycerol molecule in an adipocyte cell.

Answer 1

Lipase catalyzes the hydrolysis of fats. One molecules of triacylglycerol is hydrolyzed by hormone sensitive (HSL) lipase to generate 2-monoacylglycerol that is subsequently hydrolyzed by monoglyceride lipase to yield glycerol and fatty acids. In times of energy need, such as fasting and exercise, adipocyte lipolysis is markedly increased by catecholamines that activate Gs-coupled receptors. These receptors, in turn, activate adenylyl cyclase to generate cyclic cAMP. Rising cellular concentrations of cAMP activate protein kinase A (PKA;this PKA is cAMP dependent) that phosphorylates HSL at three serine residues (563, 659 and 660) in a 150 amino acid stretch termed the regulatory module. This regulatory module is found within the C-terminal domain of HSL, which also contains the catalytic triad. Phosphorylation results in increased hydrolytic activity , translocation of HSL from the cytosol to the lipid-droplet surface and enhanced TAG breakdown in the cell.