Human Biochemistry, Volume 2 - Murray R. 1993
Structure, Function, and Replication of Information Macromolecules
Nucleotides
Physicochemical Properties of Purine and Pyrimidine Bases
Due to The phenomenon of keto-enol tautomerism, NUCLEOTIDES can exist in either the lactim or the lactam form (Fig. 34.7), with the lactam form predominating for guanine and thymine under physiological conditions. The Significance of this fact will become apparent in our Structure/133.html">Discussion of base pairing and mutagenesis in Chapters 38 and 40.
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Fig. 34.5. Structures of two unusual naturally occurring purine bases.
Fig. 34.6. Structure of some methylxanthines commonly found in foods.
Solubility
At neutral pH, guanine exhibits the lowest solubility, followed by xanthine. Uric acid, in the form of urates, is relatively soluble at neutral pH, but becomes poorly soluble in fluids with lower pH values, such as urine. Guanine is normally absent from human urine, whereas xanthine and uric acid are its regular components. The latter two Purines frequently constitute Urinary Tract stones.
Last update: 06/08/2026
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