Nucleotides linkage isomers

The most convincing evidence in favor of a uniform 3,5-diester linkage between nucleotides has been obtained by the action of various enzymes on synthetic diesters of known constitution.218 217 Ribonuclease and spleen extracts were found to act only on nucleoside 3-(benzyl hydrogen phosphates), but not on other isomers, to give nucleoside cyclic phosphates which are broken down further to give nucleoside 3-phosphates. It is concluded, by analogy, that polynucleotides, which are substrates for these enzymes, also possess ester groupings at the 3-positions, rather than at the... 

Most of these catal3rsts are relativdy nonspecific and will attack other pyrophosphate-containing compounds. Snake venom 17J ) and potatoes 175) have been foimd to be extremely good sources of enzymes which will act on both the oxidized and reduced forms of DPN and TPN. Jacobson and Kaplan (176) have purified an enzyme from pigeon liver acetone powder which cleaves the pyridine coenzymes at the pyrophosphate linkage. It is of interest that this catalyst reacts only with the reduced and not the oxidized forms of DPN and TPN. However, the enzyme cleaves the oxidized a-isomer of DPN 177), whereas it does not cleave the enzymically active 9-isomer 176). The specificity of the enzyme appears to be due to the structure of the nucleotides rather than to the positive chaige of the pyridine nitrogen. 

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