Guanosine 5’-triphosphate GTP

G-Protein Coupling. The heterotrimeric guanosine triphosphate (GTP) binding proteins, known as G-proteins, are a principal family of proteins serving to couple membrane receptors of the G-protein family to ionic and biochemical processes. This topic is reviewed in References 63—67. 

These organisms have been used frequently in the elucidation of the biosynthetic pathway (37,38). The mechanism of riboflavin biosynthesis has formally been deduced from data derived from several experiments involving a variety of organisms (Fig. 5). Included are conversion of a purine such as guanosine triphosphate (GTP) to 6,7-dimethyl-8-D-ribityUuma2ine (16) (39), and the conversion of (16) to (1). This concept of the biochemical formation of riboflavin was verified in vitro under nonen2ymatic conditions (40) (see Microbial transformations). 

Synthesized by soluble guanylyl cyclase and particulate guanylyl cyclase from guanosine triphosphate (GTP). Nitric oxide activates soluble guanylyl cyclase to enhance cyclic GMP production that contributes to various NO actions. Cyclic GMP is hydrolyzed by phosphodiesterases. Cyclic GMP binds to and activates cGMP-dependent protein kinase, phosphodiesterases, and Cyclic Nucleotide-regulated Cation Channels. 

Guanylyl cyclases (GC) are a family of enzymes (EC 4.6.1.2) that catalyse the formation of the second messenger cyclic GMP (cGMP) from guanosine triphosphate (GTP). GCs are subdivided in soluble GCs and GCs that are membrane-bound and linked to a receptor. Activation occurs by nitric oxide (NO) and pqrtide hormones, respectively [1,2]. 

Heme (C34H3204N4Fe) represents an iron-porphyrin complex that has a protoporphyrin nucleus. Many important proteins contain heme as a prosthetic group. Hemoglobin is the quantitatively most important hemoprotein. Others are cytochromes (present in the mitochondria and the endoplasmic reticulum), catalase and peroxidase (that react with hydrogen peroxide), soluble guanylyl cyclase (that converts guanosine triphosphate, GTP, to the signaling molecule 3, 5 -cyclic GMP) and NO synthases. 

The enzyme guanylyl cyclase produces the second messenger guanosine monophosphate (3, 5 -cyclic GMP, cGMP) from guanosine triphosphate (GTP). 

The biosynthesis processes of purines, pterins, and flavins are closely related. Both pterins and flavins are synthesized via the guanosine triphosphate (GTP) purine intermediate. 

GT Glanzmann Thrombasthenia GTP Guanosine triphosphate GTP-y-S Guanarine 5 0-(3-thiotriphosphate)... 

The activated receptor combines with the G-protein in its Ggdp form, with the consequence that guanosine triphosphate (GTP) can replace previously bound guanosine diphosphate (GDP). The extent to which this can occur will be influenced by the local concentration of GTP. 

Finally, it may be possible to obtain some limited information on the mechanisms of action of agonists from the shapes of binding curves. For example, as discussed later, the binding of some agonists is affected by guanosine triphosphate (GTP), immediately suggesting the involvement of G-proteins in the transduction mechanism. 

The GDP is replaced at the nucleotide-binding site by guanosine triphosphate (GTP), which is present in a three to fourfold excess (50-300 u. I) in the cytosol. 

G proteins comprise several families of diverse cellular proteins that subserve an equally diverse array of cellular functions. These proteins derive their name from the fact that they bind the guanine nucleotides guanosine triphosphate (GTP) and guanosine diphosphate (GDP) and possess intrinsic GTPase activity. G proteins play a central role in signal transduction as well as in a myriad of cellular processes, including membrane vesicle transport,... 

The calcineurin inhibitors tacrolimus (FK 506) and cyclosporin A block the function of dynamin and are thought to be specific for clathrin-mediated uptake (50). The smal guanosine triphosphate (GTP)ase dynamin is also involved in other processes and is therefore described in section Dynamin Dependence on Liposome Uptake. ... 

Guanine Guanosine GuanyUc acid Guanosine monophosphate (GMP) Guanosine diphosphate (GDP) Guanosine triphosphate (GTP)... 

The primary function of the dtric acid cycle is oxidation of acetyl CoA to carbon dioxide. The energy released from this oxidation is saved as NADH, FADHj, and guanosine triphosphate (GTP). The overall result of the cyde is represented by the following reaction ... 

Note that this overall reaction requires three coenzymes that we encountered as metabolites of vitamins in chapter 15 NAD+, derived from lucotiiuc acid or nicotinamide FAD, derived from riboflavin and coenzyme A(CoASH), derived from pantothenic acid. In the overall process, acetyl-SCoA is oxidized to two molecules of carbon dioxide with the release of CoASH. Both NAD+ and FAD are reduced to, respectively, NADH and FADH2. Note that one molecule of guanosine triphosphate, GTP, functionally equivalent to ATP, is generated in the process. 

Such differences have been ascribed to the fact that the cyclase is linked to two distinct guanosine triphosphate (GTP) binding proteins in the cell membrane, termed Gi and Gs. The former protein inhibits the cyclase, possibly by reducing the effects of the Gs protein which stimulates the cyclase. The relationship between the posts)maptic receptor and the second messenger system is illustrated in Figure 2.4. 

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... 

There are a number of studies on the biosynthesis of various pteridines, i.e., xanthopterin (65), isoxanthopterin (67), erythropterin (73), leucopterin (68), and pterin (62) (509-511). The most important intermediate of the proposed biosynthetic pathway from guanosine triphosphate (GTP) (604) seems to be di-hydroneopterin triphosphate (H2-NTP) (605), however, because evidence has recently been accumulated indicating that pteridines such as biopterin (70), sepiapterin (81), and drosopterins (87) are synthesized from GTP (604) by way of H2-NTP (605) (Scheme 76) (5/2). 

There are several intracellular second messengers that are activated by metabotropic receptors, also referred to as G protein-coupled receptors (Duman and Nestler 1999). These receptors couple with G proteins that are heterotrimers made up of a-, (3- and y-subunits. Interaction of the G protein heterotrimer with activated receptor increases the exchange of guanosine triphosphate (GTP) for bound guanosine diphosphate (GDP), resulting in dissociation of the heterotrimer into free a and (3y subunits that in turn can regulate second messen-... 

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