Lipoprotein lipase. Mechanism of product inhibition.

The rate at which lipoprotein lipase hydrolyzes triglycerides in lipoproteins and in synthetic emulsions decreases sharply with the amount of products formed unless albumin is present. Three factors which contribute to this inhibition as follows. (a) The fatty acids and the monoglycerides formed on hydrolysis locate at the lipid-water interface of the emulsion and, since they are substrates for the enzyme, act as competitive inhibitors of triglyceride hydrolysis. (b) The enzyme forms complexes with fatty acids. Therefore, as fatty acids accumulate in the system some of the enzyme will be sequestered into enzyme-fatty acid complexes. Albumin can prevent formation of such complexes since it has a higher affinity for fatty acids than the enzyme has. (c) Activator proteins do not enhance triglyceride hydrolysis unless a fatty acid acceptor is present. The strong inhibition of the enzyme itself and the loss of lipolysis-stimulating effects of activator proteins provide a feed-back regulation of the action of the lipase on lipoproteins at the capillary endothelium, ensuring that products are not generated more rapidly than they are utilized by the tissue.