Guanosine hydrolysis

Adenylic acids o and b were each converted by trifluoroacetic anhydride into the same 2 3 -cyclic phosphate (13, R = adenin-9-yl) by Brown, Magrath, and Todd. These authors also applied this method to the synthesis of 2 3 -cyclic phosphates (13) of cytidine, uridine, and guanosine. Hydrolysis of these cyclic phosphates gave the corresponding a and b nucleotide mixtures. Markham and Smith found that, during hydrolysis of ribonucleic acid with pancreatic ribonuclease, the 2 3 -cyclic phosphates of the pyrimidine nucleosides are formed as intermediates leading to the ribonucleoside phosphates b. The also showed that 2 3 -cyclic phosphates (13) are formed by very mild, alkaline hydrolysis of ribonucleic acid. The discoveries of these a and b isomers of mononucleotides from... 

Cyclic nucleotide phosphodiesterases (PDEs) are a class of enzymes that catalyze the hydrolysis of 3, 5 -cyclic guanosine monophosphate (cGMP) or 3, 5 -cyclic adenosine monophosphate (cAMP) to 5 -guanosine monophosphate (GMP) or 5 -adenosine monophosphate (AMP), respectively. 

The effect of receptor stimulation is thus to catalyze a reaction cycle. This leads to considerable amplification of the initial signal. For example, in the process of visual excitation, the photoisomerization of one rhodopsin molecule leads to the activation of approximately 500 to 1000 transdudn (Gt) molecules, each of which in turn catalyzes the hydrolysis of many hundreds of cyclic guanosine monophosphate (cGMP) molecules by phosphodiesterase. Amplification in the adenylate cyclase cascade is less but still substantial each ligand-bound P-adrenoceptor activates approximately 10 to 20 Gs molecules, each of which in turn catalyzes the production of hundreds of cyclic adenosine monophosphate (cAMP) molecules by adenylate cyclase. 

A more complex structure is that of leinamycin 45 (Scheme 15), a material with potent cytotoxic and antitumor properties, isolated from a Streptomyces sp. A 1,2 dithiolane-3-one ring is spiro fused to a complex macrolactam96 (and references therein). Leinamycin has the remarkable ability to cleave DNA. In brief, leinamycin reacts with a thiol and, after a profound rearrangement, forms an episulfonium ion. This ion alkylates the N7 position of guanosine residues in double stranded DNA an unstable adduct is depurinated by hydrolysis of the glycosidic bond between the alkylated base and a deoxyribose residue. Some structurally less complex l,2-dithiolane-3-one 1-oxides have a similar DNA cleaving ability.97... 

All GTP binding proteins in signal transduction share a common structural element - the Ras-like domain which is responsible for the specific complexation of guanosine diphosphate and -triphosphate and which contains catalytic residues that promote GTP-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... 

This enzyme [EC 3.5.4.15], also known as guanosine aminohydrolase, catalyzes the hydrolysis of guanosine to yield xanthosine and ammonia. 

Galactose and arabinose of unknown configuration were obtained after hydrolysis of a guanosine diphosphate sugars fraction from pig milk.85 A similar fraction from strawberry leaves produced a considerable proportion of D-xylose.69... 

Ribonucleoside 2, 3 -cyclic monophosphates are isolatable intermediates, and ribonucleoside 3 -monophosphates are end products of the hydrolysis of RNA by certain ribonucleases. Other variations are adenosine 3, 5 -cyclic monophosphate (cAMP) and guanosine 3, 5 -cyclic monophosphate (cGMP), considered at the end of this chapter. 

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) ... 

Most of the properties of RNase Ti are summarized in Tables II and IV. It is a very acidic protein, active between pH 4 and 8.5 it is most active at pH 7.5 for RNA digestion (12) and at pH 7.2 for the hydrolysis of guanosine 2, 3 -cyclic phosphate (18). The purified enzyme possesses a specific activity of about 1.6 X 10 units/mg of protein. The molecular activity (standard units/jumole enzyme) has not been determined for the cleavage of a definite dinucleoside monophosphate such as GpC or for the hydrolysis of guanosine 2, 3 -cyclic phosphate. 

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