The biosynthesis of purine begins with ribose-5-phosphate, derived from the pentose phosphate pathway (PPP). First intermediate formed in this pathway. S-
phosphoribosyl-pyrophosphate (PRPP), is also an intermediate in purine salvage pathway.
o IMP (also called inosinic acid) is the first purine nucleotide, which is synthesized as the precursor of AMP (also called adenylic acid) and GMP(also called guanylic acid)
o The monophosphates (AMP and GMP) are the forms synthesized de novo, but di_ and triphosphates are the most commonly used forms. Therefore monophosphates must be converted to the corresponding di and tri-phosphates
i. Nucleoside monophosphate kinases convert nucleoside monophosphates into corresponding diphosphates. For example, adenylate kinase converts AMP to ADP while guanylate kinase converts GMP to GDP. So, monophosphate kinases are specific to the nitrogenous base. ATP is generally used as the source of energy
ii. Conversion of nucleoside diphosphates to corresponding triphosphate is catalyzed by a single enzyme called nucleoside diphosphate
kinase, which is not specific to nitrogenous base, ie. same enzyme converts ADP to ATP and GDP to GTP.
phosphoribosyl-pyrophosphate (PRPP), is also an intermediate in purine salvage pathway.
o IMP (also called inosinic acid) is the first purine nucleotide, which is synthesized as the precursor of AMP (also called adenylic acid) and GMP(also called guanylic acid)
o The monophosphates (AMP and GMP) are the forms synthesized de novo, but di_ and triphosphates are the most commonly used forms. Therefore monophosphates must be converted to the corresponding di and tri-phosphates
i. Nucleoside monophosphate kinases convert nucleoside monophosphates into corresponding diphosphates. For example, adenylate kinase converts AMP to ADP while guanylate kinase converts GMP to GDP. So, monophosphate kinases are specific to the nitrogenous base. ATP is generally used as the source of energy
ii. Conversion of nucleoside diphosphates to corresponding triphosphate is catalyzed by a single enzyme called nucleoside diphosphate
kinase, which is not specific to nitrogenous base, ie. same enzyme converts ADP to ATP and GDP to GTP.
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