Apolipoprotein C-II is a protein that plays a crucial role in lipid metabolism. It is primarily found in lipoproteins, which are particles that transport fats in the bloodstream. This protein activates an enzyme called lipoprotein lipase, which helps break down triglycerides into free fatty acids for energy use by tissues. Deficiencies in apolipoprotein C-II can lead to elevated triglyceride levels in the blood, increasing the risk of cardiovascular diseases. It is also involved in the regulation of lipid levels, making it important for maintaining overall metabolic health.