Guanosine nucleotides

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

Cech and co-workers obtained a ribozyme which had been shortened via splicing, the L-19 RNA, from the system described above in the presence of guanosine or guanosine nucleotide as a cofactor, an intron with 414 nucleotides is cut out of the precursor rRNA, the result of splicing being L-19 RNA, which contains 395 nucleotides Cech was able to show that L-19 RNA is able to shorten and lengthen other oligonucleotide chains. 

The Ras superfamily of GTP-binding proteins is composed of several subfamilies [7] which all contain the Ras-like domain of approximately 160 amino acids and 5 consensus sequences. Two of these highly conserved motifs are responsible for specific recognition of the guanosine nucleotide, and three are necessary for binding of the phosphate groups and complexation of a Mg++ ion, which is found in all Ras-like proteins. 

Access to kinetic data for the association was made possible by the introduction of fluorescence labeled guanosine-nucleotides. Particularly helpful was the attachment of the methylanthraniloyl residue (mant) at the ribose, leading to an equilibrium mixture of the mant group at the 2 - and 3 -positions [164]. Non-hydrolyzable analogues of GTP commonly used are GppNHp or GTP-yS (see Fig. 14) [164]. 

Fig. 14A-C. Guanosine-nucleotides for biophysical characterizations of Ras proteins A gua-nosinediphosphate with a methylanthraniloylester (in grey) at the 3 -position of the ribose B guanosine-5 -[/3,y-imido]-triphosphate (GppNHp) C guanosine-5 -0-(3-thiotriphosphate)...

G-proteins are so called because they bind a guanosine nucleotide, either GTP or GDP. Their transduction mechanism involves the production of a second messenger such as 3 5 cAMP, 3 5 cyclic GMP (cGMP) or IP3 and diacylglycerol (DAG), derived from AMP, GMP and phosphatidyl inositol-3,5bisphosphate respectively (Figure 4.15). It is the second messenger that initiates the downstream amplification process phase of transduction. 

Mycophenolate sodium (62 Myfortic Norvatis, 2003) is an immunosuppressant drug used to prevent rejection in organ transplantation. It is a selective, noncompetitive, reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), the rate-limiting enzyme in the de novo pathway of guanosine nucleotide synthesis. Thus, mycophenolic acid (61), originally... 

Guanosine nucleotide, redox pathways, 43 129 Guided-ion-beam mass spectrometry, metal-0X0 systems, 44 323 Gutmann donor number, 34 174 Gypsum... 

FIGURE 18. Schematic representation of the self-splicing reaction catalyzed by group 1 introns. G is the guanosine nucleotide cofactor, P a phosphate linker... 

Mycophenolate mofetil is a functionally selective cytotoxic agent for B and T lymphocytes, where it blocks the production of guanosine nucleotides required for DNA synthesis. For purine biosynthesis, B and T lymphocytes rely on de novo synthesis rather than on the salvage pathway. Lymphocytes have little or no salvage pathway as opposed to other blood marrow elements and parenchymal cells that... 

The rates of these two complementary reactions can control the amount of either AMP or GMP present in the cell. Each of these reactions is feedback-inhibited by its nucleotide product. Thus, if more adenosine nucleotides exist than guanosine nucleotides, the synthesis of AMP slows down until the purine nucleotides balance. 

B. Z. Harris, D. Kaiser and M. Singer (1998). The guanosine nucleotide (p)ppGpp initiates development and A-factor production in Myxococcus xanthus. Genes Dev., 12, 1022-1035. 

Salts of the tetrafluoroaluminate (TFA) anion have been known for many years. Yet aqueous routes to pure materials have not been established despite the substantial amount of literature available on the subject. The present review will discuss the various synthetic methods that have been employed and will demonstrate a revised method for preparing pure TFA salts. These materials are important because TFA is able to stimulate various guanosine nucleotide-binding proteins (G-proteins) and inhibit P-type ATPases by serving as a nonhydrolyzing phosphate mimic. Additionally, various TFA salts serve as precursors to aluminum trifluoride, which is used as a catalyst for chlorofluorocarbon isomerizations and fluorinations. 

IMPDH) is an enzyme involved in guanosine nucleotide synthesis required for organisms to divide and replicate. Although tiazofurin, ribavirin, and mizoribine inhibit IMPDH, they exhibit broad cellular toxicity, lack of IMPDH enzyme specificity, and sustained response in monotherapy. Immunosuppressive agents with high IMPDH enzyme specificity have been prepared to address these concerns. 

Figure 9.133 HPLC separation of (/4) guanosine nucleotides and guanosine, injected amount 5 to 10 nmol each in 5 /xL, and (B) neopterin phosphates. The mixture of neopterin phosphates injected was produced by partial hydrolysis of 16 pmol of N IP with alkaline phosphatase and addition of 2, 3 -cNMP. (From Blau and Nieder-wieser, 1983.)...

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