In chemistry, phosphorylation of a molecule is the attachment of a phosphoryl group. This process and its inverse, dephosphorylation, are critical for many cellular processes in biology. Protein phosphorylation is especially important for their function; for example, this modification activates (or deactivates) almost half of the enzymes present in Saccharomyces cerevisiae, thereby regulating their function.[1][2][3] Many proteins (between 1/3 to 2/3 of the proteome in eukaryotes[4][5]) are phosphorylated temporarily, as are many sugars, lipids, and other biologically-relevant molecules.
Phosphorylation of sugars is often the first stage in their catabolism. Phosphorylation allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter. Phosphorylation of glucose is a key reaction in sugar metabolism because many sugars are first converted to glucose before they are metabolized further.
The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by
- D-glucose + ATP → D-glucose-6-phosphate + ADP
- ĪG° = −16.7 kJ/mol (° indicates measurement at standard condition)
Researcher D. G. Walker of the University of Birmingham determined the presence of two specific enzymes in adult guinea pig liver, both of which catalyze the phosphorylation of glucose to glucose 6 phosphate.[dubious ] The two enzymes have been identified as a specific glucokinase (ATP-D-glucose 6-phosphotransferase) and non-specific hexokinase (ATP-D-hexose 6-phosphotransferase).
Hepatic cells are freely permeable to glucose, and the initial rate of phosphorylation of glucose is the rate-limiting step in glucose metabolism by the liver (ATP-D-glucose 6-phosphotransferase) and non-specific hexokinase (ATP-D-hexose 6-phosphotransferase).[6]
https://en.wikipedia.org/wiki/Phosphorylation
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