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The following points highlight the top seven types of naturally occurring nucleotides. The types are: 1. ATP & ADP 2. Cyclic GAM (cAMP or 3’, 5’ –adenosine monophosphate) 3. S-adenosylmethionine 4. Cyclic GMP (cGMP or 3′, 5′-guanosine monophosphate) 5. Inosine Monophosphate (IMP) 6. Uridine Nucleotide Derivatives (UDP md OTP) 7. Cytosine Derivatives (CMP, CDP & CTP).
Naturally Occurring Nucleotides: Type # 1.
ATP & ADP:
(a) These are the important compounds as regards their participation in oxidative phosphorylation.
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(b) ATP is the high-energy phosphate for energy requiring reactions in the cells.
(c) ATP is the most abundant intracellular free nucleotide.
(d) Its concentration in living mammalian cells is near ImM.
Naturally Occurring Nucleotides: Type # 2.
Cyclic GAM (cAMP or 3’, 5’ –adenosine monophosphate):
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(a) This is present in most animal cells.
(b) It is formed from ATP by the enzyme adenylate cyclase, the activity of which is regulated practically by hormone receptors.
(c) It mediates a series of reactions.
(d) It is destroyed in tissues by its conversion to AMP by the enzyme cAMP phosphodiesterase.
(e) The intracellular cAMP concentrations are near 1 µM.
Naturally Occurring Nucleotides: Type # 3.
S-adenosylmethionine:
(a) It serves as a form of “active” methionine.
(b) It serves as a methyl donor in many methylation reactions.
(c) It is a source of propyl amine for the synthesis of polyamines.
Naturally Occurring Nucleotides: Type # 4.
Cyclic GMP (cGMP or 3′, 5′-guanosine monophosphate):
(a) It is formed from GTP by the enzyme guanylate cyclase.
(b) It is catabolized by phosphodiesterase to produce 5′-monophosphate.
(c) It is an important intracellular signal of extracellular events.
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(d) It acts antagonistically to cAMP.
Naturally Occurring Nucleotides: Type # 5.
Inosine Monophosphate (IMP):
(a) IMP can be formed by the deamination of AMP which takes place particularly in the muscle. This IMP when reconverted to AMP results in the net production of ammonia from aspartate.
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(b) Inosine triphosphate (ITP) and Inosine diphosphate (IDP) play an important role in the formation of oxaloacetate from pyruvate and also in energy trapping reactions during oxidation of α-Ketoglutarate.
Naturally Occurring Nucleotides: Type # 6.
Uridine Nucleotide Derivatives (UDP md OTP):
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(a) These are the important coenzymes required in the metabolism of galactose to form lactose in the mammary gland and the polymerization of glucose to from glycogen. In these reactions the substrates are UDP Glucose and UDP Galactose.
(b) Another coenzyme uridine di-phos-pho-glucuronic acid (UDP Glc UA) serves as the “active” glucuronide for conjugation reactions such as the formation of bilirubin glucuronide in the liver.
(c) They are involved in the epimerization of galactose to glucose and vice versa.
(d) They also participate in the formation of high-energy phosphate compounds.
(e) UTP is the precursor for the polymerization of uridine nucleotides into RNA.
Naturally Occurring Nucleotides: Type # 7.
Cytosine Derivatives (CMP, CDP & CTP):
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(a) These derivatives are the high-energy phosphate compounds.
(b) CTP acts as the precursor for the polymerization of CMP into nucleic acids.
(c) CTP is required for the biosynthesis of phosphoglycerides in animal tissue.
(d) Ceramide and CDP-choline are responsible for the formation of sphingomyelin and other substituted sphingosines.
