Additional Functions of Nucleotides

We generally think of nucleotides as the monomers that form DNA and RNA, yet these versatile biomolecules serve a variety of additional functions. Here we briefly consider a few additional uses of nucleotides. 

Recently, the presence of single nucleotide polymorphisms (SNPs) has been reported for several types of transporter. Extensive studies have been performed on the SNPs of OATP2 [100, 101], and the SNPs identified in African- and European-Americans are indicated in Fig. 12.3. Moreover, the frequency of SNPs differed among the African-American, European-Americans and Japanese, indicating the presence of an ethnic difference in the allelic mutation of this transporter [100, 101]. In addition, some of the mutations were associated with reduced transporter function and/or abnormalities in membrane targeting [100, 102] (Fig. 12.3). It is... 

Ethnic variation in allele frequencies can lead to important differences in disease susceptibility, outcome and drug metabolism [68, 69]. In addition to single nucleotide polymorphisms, variable number of tandem repeat (VNTR) regions have been shown to have functional significance. 

In large subunit enzymes (PVC and HPII), a short segment of about 30 residues links the a-helical domain to the C-terminal domain (Fig. 8). The latter segment is a conspicuous addition to the small subunit containing about 150 residues folded into a structure that resembles flavodoxin. For example, there is a root mean square deviation of 3.0 A between flavodoxin and approximately 100 residues of the C-terminal domains of either HPII or PVC. This can be compared to the 1.8 A root mean square deviation for 134 centers between the C-terminal domains of HPII and PVC. Unlike the N-terminal end, the final C-terminal residue Ala753 is visible in the structure of HPII. The C-terminal domain contains extensive secondary structure in the form of four a-helices (al5-18) and eight fi-strands (fi9-16). Despite the obvious structural similarity to flavodoxin, there is no evidence of nucleotide binding in the domain and its function remains a mystery. 

Antigene sequences and ribozymes form two additional classes of antisense agents. However, the therapeutic potential of these agents is only now beginning to be appraised. Certain RNA sequences can function as catalysts. These so-called ribozymes function to catalyse cleavage at specific sequences in a specific mRNA substrate. Many ribozymes will cleave their target mRNA where there exists a particular triplet nucleotide sequence G-U-C. Statistically, it is likely that this triplet will occur at least once in most mRNAs. 

A polymorphic change of nucleotide T-to-C specifying an isoleucine (I) or threonine (T) at amino acid position 232 has been found in the transmembrane region of FcyRIIb (6). The functional relevance of this polymorphism is not completely understood. Seven additional polymorphisms are described in either the ligand-binding domain or intronic regions (5,6). 

The literature of metabolism in proteinoids and proteinoid microspheres is reviewed and criticized from a biochemical and experimental point of view. Closely related literature is also reviewed in order to understand the function of proteinoids and proteinoid microspheres. Proteinoids or proteinoid microspheres have many activities. Esterolysis, decarboxylation, animation, deamination, and oxido-reduction are catabolic enzyme activities. The formation of ATP, peptides or oligonucleotides is synthetic enzyme activities. Additional activities are hormonal and inhibitory. Selective formation of peptides is an activity of nucleoproteinoid microspheres these are a model for ribosomes. Mechanisms of peptide and oligonucleotide syntheses from amino acids and nucleotide triphosphate by proteinoid microspheres are tentatively proposed as an integrative consequence of reviewing the literature. 

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