Glycerol kinase, encoded by the gene GK, is a phosphotransferase involved in triglycerides and glycerophospholipids synthesis. The enzyme catalyses the chemical reaction:
The enzyme characterised from liver converts glycerol to (R)-glyceryl 1-phosphate by transferring a phosphate group from the cofactor, adenosine triphosphate (ATP), which is converted to adenosine diphosphate (ADP).
Adipocytes lack glycerol kinase so they cannot metabolize the glycerol produced during triacyl glycerol degradation. This glycerol is instead shuttled to the liver via the blood where it is: Phosphorylated by glycerol kinase to glycerol 3-phosphate. Converted from glycerol 3-phosphate to dihydroxyacetone phosphate (DHAP) via glycerol 3-phosphate dehydrogenase. DHAP can participate in glycolysis or gluconeogenesis.
Enzyme regulation This protein may use the morpheein model of allosteric regulation.
Structure Glycerol Kinase (alternative name, ATP:glycerol 3-phosphotransferase or Glycerokinase) adopts a ribonuclease H-like fold consisting of an alpha-beta 2-layer sandwich of CATH family 3.30.420.40. , there were 20 structures of this protein in the PDB, most of which are homodimeric.
Isoforms and isozymes In addition to the enzyme encoded by the gene GK (often just called Glycerol kinase) there are a number of additional forms of the enzyme found in humans and other animals, encoded by the genes GK2, GK3, and GK5. These serve other functions, with, for example, GK2, being important for mitochondrial sheath formation in sperm.
The gene GK itself also produces multiple proteins through alternative splicings, which seems to affect their location in the cell. Notably, the canonical form (isoform 3) has a transmembrane domain, and is commonly located in the outer mitochondrial membrane, while isoform 4 lacks this domain, and is thought to represent the more cytosolic variety found in adult tissues.
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