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Purine is both a very weak acid (pK a 8.93) and an even weaker base (pK a 2.39). [6] If dissolved in pure water, the pH is halfway between these two pKa values. Purine is aromatic, having four tautomers each with a hydrogen bonded to a different one of the four nitrogen atoms. These are identified as 1-H, 3-H, 7-H, and 9-H (see image of ...
Purines are biologically synthesized as nucleotides and in particular as ribotides, i.e. bases attached to ribose 5-phosphate.Both adenine and guanine are derived from the nucleotide inosine monophosphate (IMP), which is the first compound in the pathway to have a completely formed purine ring system.
Purine degradation takes place mainly in the liver of humans and requires an assortment of enzymes to degrade purines to uric acid. First, the nucleotide will lose its phosphate through 5'-nucleotidase. The nucleoside, adenosine, is then deaminated and hydrolyzed to form hypoxanthine via adenosine deaminase and nucleosidase respectively.
The secondary structure is responsible for the shape that the nucleic acid assumes. The bases in the DNA are classified as purines and pyrimidines. The purines are adenine and guanine. Purines consist of a double ring structure, a six-membered and a five-membered ring containing nitrogen. The pyrimidines are cytosine and thymine. It has a ...
Purine nucleoside phosphorylase (PNPase) Nucleotidyltransferases (EC 2.7.7) Enzymes that have phosphorolytic 3' to 5' exoribonuclease activity (break phosphodiester bond) RNase PH; Polynucleotide Phosphorylase (PNPase) All known phosphorylases share catalytic and structural properties. [2]
Depurination is not uncommon because purine is a good leaving group via the 9N-nitrogen (see the structure of a purine).Furthermore, the anomeric carbon is especially reactive towards nucleophilic substitution (effectively making the carbon-oxygen bond shorter, stronger and more polar, while making the carbon-purine bond longer and weaker).
De novo biosynthesis of purine nucleotides is fairly complex, consisting of several enzymatic reactions. Utilizing the five-ring sugar structure as a base, the purine ring is built a few atoms at a time in an eleven-step process that leads to the formation of inosinate (IMP).
In enzymology, a purine nucleosidase (EC 3.2.2.1) is an enzyme that catalyzes the chemical reaction a purine nucleoside + H 2 O ⇌ {\displaystyle \rightleftharpoons } D-ribose + a purine base Thus, the two substrates of this enzyme are purine nucleoside and H 2 O , whereas its two products are D-ribose and purine base .