Lipoprotein lipase migration

Peripheral tissues uch as muscle, adipose tissue, and the I acta ting breast contain both hoTmone-sensitive lipnse and lipoprotein lipase. This second lipase, mentioned in the lipoprotein section of Chapter ft, requires apolipoprotein C-II as a cofactor. The lipase is secreted by cells and migrates through the interstitial fluid to the capillary, where it becomes bound to the membrane with its active site exposed to the bloodstream. This binding to the luminal wall of the capillary occurs by attachment to a polymer called glycosaminoglycan. 

Lipoprotein lipase may be activated by changes in plasma glucagon and insulin. This activation appears to occur by an increase in migration of the enzyme to the capillary wall. For example, a decrease in the glucagon/insulin ratio, as with feeding, may provoke an increase in the proportion of enzyme located on the luminal wall and a decrease in the proportion that is intracellular. Feeding appears to provoke activation of the enzyme in adipose tissue, but not of the enzyme located in muscle or other hssues. 

Activation of lipoprotein lipase at the cell surface. As shown in Table 9.2, lipoprotein lipase has a very short half-life, of the order of 1 hour. In response to insulin acting on adipocytes there is induction of enzyme synthesis. The newly synthesized enzyme then migrates to the surface of the blood vessel endothelial walls, where it binds chylomicrons or VLDL (section 5.6.2) and catalyses the hydrolysis of triacylglycerol. The non-esterified fatty acids are mainly taken up by adipose tissue and used for synthesis of triacylglycerol. 

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