UMPS,

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Another property of pyrimidines and purines is their strong absorbance of ultraviolet (UV) light, which is also a consequence of the aromaticity of their heterocyclic ring structures. Figure 11.8 shows characteristic absorption spectra of several of the common bases of nucleic acids—adenine, uracil, cytosine, and guanine—in their nucleotide forms AMP, UMP, CMP, and GMP (see Section 11.4). This property is particularly useful in quantitative and qualitative analysis of nucleotides and nucleic acids. 

FIGURE 11.13 Structures of the four cotntnou ribonucleotides—AMP, GMP, CMP, and UMP—together with their two sets of full uatnes, for example, adeuosiue 5 -mouophosphate and adenylic acid. Also shown is the nucleoside 3 -AMP. 

Analogously to MP methods, coupled cluster theory may also be based on a UFIF reference wave function. The resulting UCC methods again suffer from spin contamination of the underlying UHF, but the infinite nature of coupled cluster methods is substantially better at reducing spin contamination relative to UMP. Projection methods analogous to those of the PUMP case have been considered but are not commonly used. ROHF based coupled cluster methods have also been proposed, but appear to give results very similar to UCC, especially at the CCSD(T) level. 

Fungal chitin synthases are found as integral proteins of the plasma membrane and in chitosomes a divalent cation, Mg(II), is necessary for enzyme activity but neither primers nor a hpid intermediate are required. The substrate and free GlcNAc activate the allosteric enzyme. UDP, the byproduct of the enzymatic activity, is strongly inhibitory to chitin synthase however, it may be metabohzed readily to UMP by a diphosphatase. 

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