Succinyl-CoA synthetase: Difference between revisions
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<applet load='1cqj' size='300' frame='true' align='right' caption='Structure of succinyl-CoA synthetase' /> | <applet load='1cqj' size='300' frame='true' align='right' caption='Structure of succinyl-CoA synthetase' /> | ||
'''Succinyl-Coa synthetase''' catalyzes the reversible reaction of succinyl-CoA + NDP + Pi <-> succinate + CoA + NTP (where N is either adenosine or guanosine. It can be found in Escherichia coli. | '''Succinyl-Coa synthetase''' catalyzes the reversible reaction of succinyl-CoA + NDP + Pi <-> succinate + CoA + NTP (where N is either adenosine or guanosine. It can be found in Escherichia coli. It is the fifth step in the citric acid cycle. | ||
==Structure== | ==Structure== | ||
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The histidine residue involved in the (de)phosphorylation of (ATP)ADP acts through the following mechanism. | The histidine residue involved in the (de)phosphorylation of (ATP)ADP acts through the following mechanism. | ||
[[Image:Synthetase_mechanism.jpg]] | [[Image:Synthetase_mechanism.jpg]] | ||
A cooperative binding catalysis mechanism has been proposed and it has been shown that binding of ATP at one catalytic site promotes catalytic activity at another catalysis site.<ref>PMID:6997289</ref> It has been shown that the enzyme will bind with ATP in the presence of Mg+2 to form a complex containing 2 ATP residues as well as 2 phosphoric acid residues, after incubation this the complex converts to another one containing 4 phosphoric residues per protein. Only the second complex reacts with succinate and CoA to form the succinyl-CoA complex which then releases as many phosphoric residues as bound succinate.<ref>PMID:570066</ref> A transfer of the phosphoric residue from the first active site is seen to be coordinate with a transfer of a phosphoric residue to the second active site suggesting again a cooperative binding catalysis. This cooperative catalysis means that the presence of ATP or ADP can be both activating and inhibiting depending on the stage of catalysis they interact with the enzyme. | A cooperative binding catalysis mechanism has been proposed and it has been shown that binding of ATP at one catalytic site promotes catalytic activity at another catalysis site.<ref>PMID:6997289</ref> It has been shown that the enzyme will bind with ATP in the presence of Mg+2 to form a complex containing 2 ATP residues as well as 2 phosphoric acid residues, after incubation this the complex converts to another one containing 4 phosphoric residues per protein. Only the second complex reacts with succinate and CoA to form the succinyl-CoA complex which then releases as many phosphoric residues as bound succinate.<ref>PMID:570066</ref> A transfer of the phosphoric residue from the first active site is seen to be coordinate with a transfer of a phosphoric residue to the second active site suggesting again a cooperative binding catalysis. This cooperative catalysis means that the presence of ATP or ADP can be both activating and inhibiting depending on the stage of catalysis they interact with the enzyme. | ||
After the Succinyl-CoA has been phosphorylated and subsequently dephosphorylated it is release as succinate which continues along the Krebs cycle. | |||
==Bound Form of Succinyl-CoA synthetase== | ==Bound Form of Succinyl-CoA synthetase== | ||
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The form of succinyl-CoA synthetase shown here (PDB code 1CQI) is the bound form with two <scene name='Lucas_Hamlow_sandbox_1/Adp-mg_complex/1'>ADP-Mg complexes</scene> (the ADP is highlighted and the Mg is in green).<ref>PMID:10625475</ref> As seen here, the <scene name='Lucas_Hamlow_sandbox_1/His_246_near_pi_group/1'>Histidine 246</scene> residues on both the alpha and beta subunits are present and interacting with the lone Pi group while the ADP group is bound elsewhere on the subunit. | The form of succinyl-CoA synthetase shown here (PDB code 1CQI) is the bound form with two <scene name='Lucas_Hamlow_sandbox_1/Adp-mg_complex/1'>ADP-Mg complexes</scene> (the ADP is highlighted and the Mg is in green).<ref>PMID:10625475</ref> As seen here, the <scene name='Lucas_Hamlow_sandbox_1/His_246_near_pi_group/1'>Histidine 246</scene> residues on both the alpha and beta subunits are present and interacting with the lone Pi group while the ADP group is bound elsewhere on the subunit. | ||
==Kinetics== | |||
As stated earlier, the presence of GTP, GDP, ATP, and ADP can be either activating or inhibiting depending on the stage of catalysis it interacts with the enzyme. | |||
==Regulation== | |||
Succinyl-CoA synthetase is not a major regulator in the Krebs cycle, making it dependent on the steps prior. | |||