Triacylglycerol Metabolism

Hydrolysis of Triacylglycerol (Lipolysis)

• Triacylglycerols are broken down into fatty acids and glycerol by hormone-sensitive lipase enzyme.
• This breakdown occurs mainly in adipose tissue, releasing free fatty acids into the plasma.
• Free fatty acids are then taken up by tissues (except the brain) to be oxidized or re-esterified.
• Glycerol utilization depends on the presence of glycerol kinase enzyme in tissues such as liver, kidney, intestine, brown adipose tissue, and lactating mammary gland.

Triacylglycerol Biosynthesis

• Triacylglycerols are formed by combining glycerol with three fatty acids.
• The initial step in triacylglycerol formation is the activation of both fatty acids and glycerol.
• Multiple reaction steps follow, ultimately leading to the formation of triacylglycerol.

Activation of Glycerol

• Glycerol kinase enzyme catalyzes the activation of glycerol to glycerol 3-phosphate.
• In the absence or low activity of glycerol kinase enzyme (e.g., in muscle or adipose tissue), glycerol 3-phosphate is formed from dihydroxyacetone phosphate (produced from glycolysis).
• This reaction is catalyzed by glycerol-3-phosphate dehydrogenase enzyme, establishing a crucial connection between carbohydrate and lipid metabolism.