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Glycerol kinase, encoded by the gene GK, is a phosphotransferase enzyme involved in triglycerides and glycerophospholipids synthesis. Glycerol kinase catalyzes the transfer of a phosphate from ATP to glycerol thus forming glycerol 3-phosphate :
Triglycerides are built from three fatty acids, esterified onto each of three hydroxy groups of glycerol, which is derived from glycerol 3-phosphate.In mammals, glycerol 3-phosphate is usually synthesized through glycolysis, a metabolic pathway that degrades glucose into fructose 1,6-bisphosphate and then into two molecules of dihydroxyacetone phosphate, which beget glycerol 3-phosphate and ...
The DHAP formed during fructolysis can also be converted to glycerol and then glycerol 3-phosphate for TG synthesis. Thus, fructose can provide trioses for both the glycerol 3-phosphate backbone, as well as the free fatty acids in TG synthesis. Indeed, fructose may provide the bulk of the carbohydrate directed toward de novo TG synthesis in ...
The free fatty acids and glycerol are then released into the blood. The activity of hormone sensitive lipase is regulated by the circulating hormones insulin, glucagon, norepinephrine, and epinephrine. Lipolysis can be regulated through cAMP's binding and activation of protein kinase A (PKA). PKA can phosphorylate lipases, perilipin 1A, and CGI ...
Three fatty acid chains are bonded to each glycerol molecule. Each of the three -OH groups of the glycerol reacts with the carboxyl end of a fatty acid chain (-COOH). Water is eliminated and the remaining carbon atoms are linked by an -O- bond through dehydration synthesis. Both the adipose tissue and the liver can synthesize triglycerides.
The cAMP activates a protein kinase, which phosphorylates and thus, in turn, activates a hormone-sensitive lipase in the fat cell. This lipase cleaves free fatty acids from their attachment to glycerol in the fat stored in the fat droplet of the adipocyte. The free fatty acids and glycerol are then released into the blood.
Global control of gluconeogenesis is mediated by glucagon (released when blood glucose is low); it triggers phosphorylation of enzymes and regulatory proteins by Protein Kinase A (a cyclic AMP regulated kinase) resulting in inhibition of glycolysis and stimulation of gluconeogenesis. Insulin counteracts glucagon by inhibiting gluconeogenesis.
Glycerol 3-phosphate is a starting material for de novo synthesis of glycerolipids. In eukaryotes, it is first acylated on its sn-1 position by an ER- or mitochondrial membrane enzyme, glycerol-3-phosphate O-acyltransferase. A second acyl group is subsequently installed on the sn-2 position making phosphatidic acids.