Deoxyguanylate

The chemical nature of the monomeric deoxynucleo-tide units of DNA—deoxyadenylate, deoxyguanylate, deoxycytidylate, and thymidylate—is described in Chapter 33. These monomeric units of DNA are held in polymeric form by 3 5 -phosphodiester bridges constituting a single strand, as depicted in Figure 35-1. 

ATP GMP phosphotransferase GMP kinase deoxyguanylate kinase guanosine monophosphate kinase kinase, guanylate (phosphorylating)... 

DNA is a linear polymer of covalently joined deoxyribonucleotides, of four types deoxyadenylate (A), deoxyguanylate (G), deoxycytidy-late (C), and deoxythymidylate (T). Each nucleotide, with its unique three-dimensional structure, can associate very specifically but non-covalently with one other nucleotide in the complementary chain A always associates with T, and G with C. Thus, in the double-stranded DNA molecule, the entire sequence of nucleotides in one strand is complementary to the sequence in the other. The two strands, held together by hydrogen bonds (represented here by vertical blue lines) between each pair of complementary nucleotides, twist about each other to form the DNA double helix. In DNA replication, the two strands separate and two new strands are synthesized, each with a sequence complementary to one of the original strands. The result is two double-helical molecules, each identical to the original DNA. 

Guanine, G Guanylic acid, GMP Deoxyguanylic acid, dGMP... 

ECO RI ENDONUCLEASE. Eco RI endonuclease is one of the better studied endonucleases. It is a small protein of 276 amino acid residues (31,065 daltons) of known sequence (6,7). The active enzyme contains two subunits (8,9) and hydrolyzes the phospho-diester bond between the deoxyguanylic and deoxyadenylic acid residues of duplex 5 -GAATTC-3. On hydrolysis, there is an... 

The abbreviated notations pApCpG or pACG denote a trinucleotide of DNA consisting of the building blocks deoxyadenylate monophosphate, deoxycytidylate monophosphate, and deoxyguanylate monophosphate linked by a... 

Thus, the symbol ACG indicates that the unlinked 5 -OH group is on deoxyadenylate, whereas the unlinked 3 -OH group is on deoxyguanylate. Because of this polarity, ACG and GCA correspond to different compounds. 

Adenine (A) Deoxyadenosine Guanine (G) Deoxyguanosine Thymine (T) Thymidine Cytosine (C) Deoxycytidine Deoxyadenylate (dAMP) Deoxyguanylate (dGMP) Thymidylate (TMP) Deoxycytidylate (dCMP)... 

DNA contains the bases adenine A), thymine (T), guanine (G), and cytosine (C). These bases are covalently attached to the deoxyribose phosphate to form nucleotides. The respective nucleotides are called dcoxyadenylic add (dA), deoxythy-midylic add (dT), deoxyguanylic acid (dC), and deoxycj tidylic acid (dC). The prefix "deoxy" indicates that the sugar is deoxyribose, rather than ribo e. The word "acid" indicates that the ribose con tains a covalently bound phosphoric acid group. 

Using the same rationale as is used above in the purine section, it can be seen from the results in the Table that an extensive back reaction of the deoxyguanylic acid -(Cl2") radical occurs. The slight radioprotective effect of chloride in acidic solutions of deoxycytidylic acid and deoxyadenylic acid may be caused by the inability of these compounds to react with Cl2". 

The rate constants for reaction of the Cl2" radical with the compounds investigated are much lower than the corresponding OH radical rate constants. The Cl2" rate constants for reaction with this series of compounds vary over a wider range than do their OH radical counterparts. The effect of this range of rate constants will be most evident in the radiolysis of mixtures of compounds. In the radiolysis of a mixture of equal concentrations of the deoxynucleotides, OH radicals cause approximately equal destruction of all four bases (4). Cl2" radicals, on the other hand, will react preferentially with deoxyguanylic acid and only a tenth of these reactions will cause base destruction. Thus, the net effect of conversion of OH radicals to Cl2" radicals, in this system, will be... 

Guanine G Guanylic acid GMP Deoxyguanylic acid dGMP... 

Guanylate kinase has been partly purified from hog brain 10), from Escherichia coli 11), and from a transplantable mouse tumor, Sarcoma 180 12). These preparations show similarities with respect to substrate specificity and cation requirements, but differ with respect to pH optima and molecular weight. All three preparations are highly specific in that guanylate and deoxyguanylate are phosphorylated, but adenylate, ino-sinate, xanthylate, and cytidylate are not substrates. The brain and tumor enzymes also phosphorylate 8-azaguanylate. ATP or dATP are the specific phosphate donors for the three enzymes. 

The acceptability of deoxyguanylate and dATP as substrates in the guanylate kinase reaction is noteworthy there does not appear to be a particular group of nucleoside monophosphate kinases specific for deoxyribonucleotides (see Chapter 14), apart from that for thymidylate and deoxyuridylate. 

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