Stored triacylglycerol and cholesterol are released by
Lipolysis The prevailing state of high glucagon-insulin ratio stimulates cAMP-mediated lipolysis by increasing the activity of hormone-sensitive lipase. Then skeletal muscle, hea, and kidney will shut down their glucose utilization; and will depend mainly on fatty acids for energy needs (glucose-fatty acid cycle). Inactivation of pyruvate dehydrogenase by phosphorylation is the basis of this change. The stimulation of the activity of CAT by glucagon ors increased rate of beta-oxidation. The increased rate of lipolysis and beta-oxidation provides an alternate source of fuel as acetyl CoA and subsequently ketone bodies. Ketone bodies provide fuel fortissues like hea muscle, skeletal muscle and to some extent the brain. It is seen that brain stas utilizing ketone bodies from 3rd day of starvation. By 10th day of starvation, about 60% of energy for brain is derived from ketone bodies. The cyclic AMP-mediated activation cascade enhances the intracellular hormone-sensitivelipase (Fig. 11.16 and Table 11.4). The phosphorylated form of the enzyme is active which acts on TAG and liberates fatty acids. iii. Under conditions of starvation, a high glucagon, ACTH, glucocoicoids and thyroxine have lipolytic effect. The released free fatty acids (FFA) are taken up by peripheral tissues as a fuel. Ref: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 89,140
Lysosomal lipase
Lipoprotein lipase
LCAT
Hormone sensitive lipase
Metabolism of lipid