Guanosine 5 - triphosphate

Receptors linked to guanylyl cyclase and which catalyze the formation of guanosine triphosphate (GMP) to guanosine-3A -cychc monophosphate (cychc GMP) include those for atrial natriuretic factor (ANF) and endothehal-derived relaxing factor (EDRF), mediating vasodilatation, and nitric oxide [10102 3-9], NO, or a clearly related derivative. 

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)... 

Figure 12 Gradient separation of bases, nucleosides and nucleoside mono- and polyphosphates. Column 0.6 x 45 cm. Aminex A-14 (20 3 p) in the chloride form. Eluent 0.1 M 2-methyl-2-amino-l-propanol delivered in a gradient from pH 9.9-100 mM NaCl to pH 10.0-400 mM NaCl. Flow rate 100 ml/hr. Temperature 55°C. Detection UV at 254 nm. Abbreviations (Cyt) cytosine, (Cyd) cytidine, (Ado) adenosine, (Urd) uridine, (Thyd) thymidine, (Ura) uracil, (CMP) cytidine monophosphate, (Gua) guanine, (Guo) guanosine, (Xan) xanthine, (Hyp) hypoxanthine, (Ino) inosine, (Ade) adenosine, (UMP) uridine monophosphate, (CDP) cytidine diphosphate, (AMP) adenosine monophosphate, (GMP) guanosine monophosphate, (IMP) inosine monophosphate, (CTP) cytidine triphosphate, (ADP) adenosine diphosphate, (UDP) uridine monophosphate, (GDP) guanosine diphosphate, (UTP) uridine triphosphate, (ATP) adenosine triphosphate, (GTP), guanosine triphosphate. (Reproduced with permission of Elsevier Science from Floridi, A., Palmerini, C. A., and Fini, C., /. Chromatogr., 138, 203, 1977.)...

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. 

The answer is e. (Katzung, p 842.) Ribavirin most likely interferes with guanosine triphosphate synthesis, resulting in inhibition of capping of viral messenger RNA and viral RN A-dependent RNA polymerase. It is effective in moderating infections with respiratory syncytial virus. 

GnRI I—gonadotropin-releasing hormone GTP—guanosine triphosphate GU—genitourinary h—hour(s)... 

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,... 

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