Guanosine triphosphate hydrolysis

The product succinyl-CoA is able to participate in ATP synthesis as an example of substrate-level phosphorylation - we met some other examples in the glycolytic pathway. Essentially, hydrolysis of succinyl-CoA liberates snfficient energy that it can be coupled to the synthesis of ATP from ADP. However, guanosine triphosphate (GTP) is the... 

The hydrolysis of the acyl CoA in the first step is used for energy storage by conversion of guanosine diphosphate (GDP) to guanosine triphosphate (GTP) ... 

Schweins, T., Geyer, M., Kalbitzer, H. R., Wittinghofer, A., and Warshel, A. (1996). Linear free energy relationships in the intrinsic and GTPase activating protein-stimulated guanosine 5 -triphosphate hydrolysis of p21ras. Biochemistry 35, 14225-14231. 

STEPS s-6 Hydrolysis and dehydrogenation of succinyl CoA. Succinyl CoA is hydrolyzed to succinate in step 5. The reaction is catalyzed by succinyl CoA synthetase and is coupled with phosphorylation of guanosine diphosphate (GDP) to give guanosine triphosphate (GTP). The overall transformation is similar to that of step 8 in glycolysis (Figure 29.4), in which a thiol ester is converted into an acyl phosphate and a phosphate group is then transferred to ADP. 

The activity of G-proteins is regulated by the binding and hydrolysis of guanosine triphosphate (GTP) by the Ga subunit. If guanosine diphosphate (GDP) is bound to the a subunit, it will associate with the fy subunits, but the trimer is inactive. When a cell receptor is activated, the trimer releases GDP and the a subunit is able to bind GTP. After binding GTP the a subunit dissociates from the py subunit and from the receptor. Either the a-GTP complex or the fy subunits can then activate downstream effectors. Thus, defects in any of the numerous G-proteins may alter cellular biochemistry and cause disease. 

Some biosynthetic reactions are driven by the hydrolysis of nucleoside triphosphates that are analogous to ATP—namely, guanosine triphosphate (GTl ), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The diphosphate forms of these nucleotides are denoted by GDP, UDP, and CDP, and the monophosphate forms are denoted by GMP, UMP, and CMP. Enzymes catalyze the transfer of the terminal phosphoryl group from one nucleotide to another. The phosphorylation of nucleoside monophosphates is catalyzed by a family of nucleoside monophosphate kinases, as discussed in Section 9.4. The phosphorylation of nucleoside diphosphates is catalyzed by 7iucleoside diphosphate kinase, an enzyme with broad... 

Closely related to ATP, and present in biological systems, are a number of other nucleoside triphosphates and their corresponding diphosphates and monophosphates. These are uridine triphosphate (UTP), cytidine triphosphate (CTP), guanosine triphosphate (GTP), and thymidine triphosphate (TTP), all of which have about the same free energy of hydrolysis as ATP (11.29). In addition there are the deoxy nucleoside triphosphates (Chapter 10.4). 

Microtubules are polymeric fibers that play a key role in cell division and in cell shape and motility. They are formed from subunits of the protein tubulin (molecular weight about 100 kd), which assemble into protofilaments. Each microtubule is composed of thirteen linked protofilaments. Intermediate in size are oligomers, which are short stretches of protofilaments (Correia and Williams, 1983). The assembly of microtubules is driven by the hydrolysis of the nucleotide guanosine triphosphate (GTP), which binds to the tubulin subunits and hydrolyzes to the diphosphate (GDP) on polymerization. The GDP can also bind to tubulin, but it inhibits microtubule assembly. The nucleotides are rapidly exchangeable when bound to tubulin, but become nonexchangeable when attached either to oligomers or to microtubules. 

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