Adenosine monophosphate binding sites

A sequence stretch 300 base pairs upstream of the transcriptional start site suffices for most of the transcriptional regulation of the IL-6 gene (Fig. 1). Within this sequence stretch several transcription factors find their specific recognition sites. In 5 to 3 direction, AP-1, CREB, C/EBP 3/NF-IL6, SP-1 and NF-kB can bind to the promoter followed by TATA and its TATA binding protein TBP. Most enhancer factors become active in response to one or several different stimuli and the active factors can trigger transcription individually or in concert. For example, AP-1 is active upon cellular stress, or upon stimuli that tell cells to proliferate CREB becomes also active if cells experience growth signals, but also upon elevation of intracellular levels of cyclic adenosine monophosphate (cAMP), which occurs upon stimulation if so called hormone-activated G protein-coupled receptors. 

A model of adenosine monophosphate (AMP) bound to the AMP binding site was built by first overlaying AMP on ZMP in the enzyme subunit C4 (Figure 2). The model was then energy minimized using 500 steps of... 

The activation of adenylyl cyclase enables it to catalyze the conversion of adenosine triphosphate (ATP) to 3 5 -cyclic adenosine monophosphate (cAMP), which in turn can activate a number of enzymes known as kinases. Each kinase phosphorylates a specific protein or proteins. Such phosphorylation reactions are known to be involved in the opening of some calcium channels as well as in the activation of other enzymes. In this system, the receptor is in the membrane with its binding site on the outer surface. The G protein is totally within the membrane while the adenylyl cyclase is within the membrane but projects into the interior of the cell. The cAMP is generated within the cell (see Rgure 10.4). 

The use of paramagnetic ions to examine the binding sites and solution conformations of nucleosides and nucleotides is becoming very widespread. Studies that describe the complexing of a variety of nucleosides and nucleotides with paramagnetic ions involve the use of Mn(ii), (749-751) Cu(ii), (750, 752-754) and lanthanide ions. (755) Mn " ions appear to bind to multiple sites on purine and pyrimidine nucleosides (749) whereas the phosphate group is the primary binding site on monophosphate nucleotides. (750) relaxation studies indicate that Cu " ions bind to N-3 of 5 -cytidine monophosphate (5 -CMP). In contrast to cytidine [59], adenosine [60] appears to have... 

Moreover, some allosteric eri2ymes may be stimulated by modulator molecules. These molecules are not the end product of a series of reactions, but rather may be the substrate molecule itself. These en mes have two or more substrate binding sites, which serve a dual function as both catalytic sites and regulatory sites. Such allosteric enemies respond to excessive concentrations of substrates that must be removed. Furthermore, some en mes have two or more modulators that may be opposite in effect and have their own specific allosteric site. When occupied, one site may speed up the catalytic reaction, while the other may slow it down. ADP and AMP (adenosine monophosphate) stimulate certain metabolic pathway eri2ymes, for example, while ATP inhibits the same allosteric eri2ymes. 

For our initial studies, we chose inosine (I) and adenosine monophosphate (AMP), Figure 3. Only the former has the possibility of N7-06 chelation. We chose to work at low pH s of ca. 2 where all the literature evidence seemed to point to N7 as the only binding site on both I and AMP (24>25). Acidic solutions... 

Figure i. Molecular structures of inosine (left) and adenosine 5 -monophosphate (right). At acidic pH values, the only Pt binding site expected is N7,... 

Phosphofructokinase activity is sensitive to both positive and negative allosterism. For instance, when ATP is present in abundance, a signal that the body has sufficient energy, it binds to an effector binding site on phosphofructokinase. This inhibits the activity of the enzyme and, thus, slows the entire pathway. An abundance of AMP (adenosine monophosphate), which is a precursor of ATP, is evidence that the body needs to make ATP to have a sufficient energy supply. When AMP binds to an effector binding site on phosphofructokinase, enzyme activity is increased, speeding up the reaction and the entire pathway. 

The synthesis of the two diastereoisomers of P -l-(2-nitrophenyl)ethyl adenosine S -lri-phosphate (91) has been achieved using resolved (R)- and (5)-l-(2-nilroidienyl)ethanol. The alcohols were converted to (R)- and (5)-l-(2-nitrophenyl)ethyl phosphates by phosphitylation with N,)V-diisopropyl-fi(s-(2-cyanoethyl)phosphoramidite (92) and subsequent oxidation with 3-chlorobenzoic acid. Each of the monophosphates was activated with carbonyidiimidazole and condensed with adenosine diphosphate to give the desired triphosphate. These ATP analogues can be used for the rapid release (by flash photolysis) of ATP in biological systems. The 8-azido-3 -0-anthraniloyl derivatives of 2 -dADP (93) and 2 -dATP (94) have been prepared in seven steps from 8-azido-2 -deoxyadenosine. These compounds are of interest as fluorescent and photoactivatable probes for the nucleotide binding site of kinases and cyclases. In particular, (94) was shown to be a competitive inhibitor of Bordetella pertussis adenylate cyclase and the observed K- (74 pM) was close to tiiat predicted from the K- value of 3 -0-anthraniloyl-2 -dATP. ... 

The H2 receptor is a 359-amino-acid protein in humans. It has some features similar to the Hi protein (e.g., N-terminal glycosylation sites) and phosphorylation sites in the C-terminal. An aspartic acid residue in the third transmembrane loop appears to be critical to agonist and antagonist binding, and threonine/aspartate and tyrosine/aspartate couples in the fifth transmembrane domain appear to be important for interaction of the imidazole part of the histamine molecule. It is positively coupled via Gas to activate adenylyl cyclase for synthesis of cyclic adenosine monophosphate (cAMP) as a second messenger. In some systems, it is coupled through Gq proteins to stimulate phospholipase C. It appears in some cells that other processes, such as breakdown of phosphoinositides, control of intracellular calcium ion levels, and phospholipase A2 activity, can be regulated by other cAMP-independent pathways. 

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