Regulation and Control
It has long been held that hormone-sensitive lipase (HSL) is the enzyme that hydrolyses triacylglycerides to free fatty acids from fats (lipolysis). However, more recently it has been shown that at most HSL converts triacylglycerides to monoglycerides and free fatty acids. Monoglycerides are hydrolyzed by monoglyceride lipase; adipose triglyceride lipase may have a special role in converting triacylglycerides to diacylglycerides, while diacylglycerides are the best substrate for HSL. HSL is regulated by the hormones insulin, glucagon, norepinephrine, and epinephrine.
Glucagon is associated with low blood glucose, and epinephrine is associated with increased metabolic demands. In both situations, energy is needed, and the oxidation of fatty acids is increased to meet that need. Glucagon, norepinephrine, and epinephrine bind to G protein-coupled receptors that activate adenylate cyclase to produce cyclic AMP. As a consequence, cAMP activates protein kinase A, which phosphorylates (and activates) hormone-sensitive lipase.
When blood glucose is high, lipolysis is inhibited by insulin. Insulin activates protein phosphatase 2A, which dephosphorylates HSL, thereby inhibiting its activity. Insulin also activates the enzyme phosphodiesterase, which breaks down cAMP and stops the re-phosphorylation effects of protein kinase A.
For the regulation and control of metabolic reactions involving fat synthesis, see lipogenesis.
Read more about this topic: Fatty Acid Metabolism
Famous quotes containing the words regulation and/or control:
“Nothing can be more real, or concern us more, than our own sentiments of pleasure and uneasiness; and if these be favourable to virtue and unfavourable to vice, no more can be requisite to the regulation of our conduct and behavior.”
—David Hume (1711–1776)
“Knowledge in the form of an informational commodity indispensable to productive power is already, and will continue to be, a major—perhaps the major—stake in the worldwide competition for power. It is conceivable that the nation-states will one day fight for control of information, just as they battled in the past for control over territory, and afterwards for control over access to and exploitation of raw materials and cheap labor.”
—Jean François Lyotard (b. 1924)