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QuickView for Phosphoenolpyruvate carboxykinase, GTP-utilising, C-terminal (biogroup)
- Description:
- Phosphoenolpyruvate carboxykinase (PEPCK) catalyses the first committed (rate-limiting) step in hepatic gluconeogenesis, namely the reversible decarboxylation of oxaloacetate to phosphoenolpyruvate (PEP) and carbon dioxide, using either ATP or GTP as a source of phosphate. The ATP-utilising and GTP-utilising enzymes form two divergent subfamilies, which have little sequence similarity but which retain conserved active site residues. ATP-utilising PEPCKs are monomers or oligomers of identical subunits found in certain bacteria, yeast, trypanosomatids, and plants, while GTP-utilising PEPCKs are mainly monomers found in animals and some bacteria. Both require divalent cations for activity, such as magnesium or manganese. One cation interacts with the enzyme at metal binding site 1 to elicit activation, while the second cation interacts at metal binding site 2 to serve as a metal-nucleotide substrate. In bacteria, fungi and plants, PEPCK is involved in the glyoxylate bypass, an alternative to the tricarboxylic acid cycle. PEPCK helps to regulate blood glucose levels. The rate of gluconeogenesis can be controlled through transcriptional regulation of the PEPCK gene by cAMP (the mediator of glucagon and catecholamines), glucocorticoids and insulin. In general, PEPCK expression is induced by glucagon, catecholamines and glucocorticoids during periods of fasting and in response to stress, but is inhibited by (glucose-induced) insulin upon feeding. With type II diabetes, this regulation system can fail, resulting in increased gluconeogenesis that in turn raises glucose levels.PEPCK consists of an N-terminal and a catalytic C-terminal domain, with the active site and metal ions located in a cleft between them. Both domains have an alpha/beta topology that is partly similar to one another. Substrate binding causes PEPCK to undergo a conformational change, which accelerates catalysis by forcing bulk solvent molecules out of the active site. PCK uses an alpha/beta/alpha motif for nucleotide binding, this motif differing from other kinase domains. GTP-utilising PEPCK has a PEP-binding domain and two kinase motifs to bind GTP and magnesium.This entry represents the C-terminal P-loop domain found in GTP-utilising phosphoenolpyruvate carboxykinase enzymes.
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