424 D. M. BROWN AND A. R. TODD 



from the demonstration" •^^•^'"' that in addition to larger fragments, sub- 

 substantial amounts of pyrimidine mononucleotides were formed by ribo- 

 nuclease digestion without the concomitant production of purine mono- 

 nucleotides. A single claim to have isolated purine mononucleotides from 

 ribonuclease digests^"^ has not been confirmed by later work. Further evi- 

 dence for a specificity of ribonuclease towards pyrimidine nucleotide resi- 

 dues came from the work of Schmidt, Thannhauser, and their co-workers. 

 It was found^'''''^*'^ that after exhaustive digestion of ribonucleic acid with 

 ribonuclease and subsequent treatment with prostatic phosphomonoester- 

 ase, inorganic phosphate was produced in an amount corresponding to at 

 least 93 % of the pyrimidine nucleotide phosphorus content of the original 

 nucleic acid. The remaining organically bound phosphorus was present 

 entirely, or almost entirely, as purine nucleotide phosphorus.'*'^ The con- 

 clusion was drawn that in ribonuclease digests the pyrimidine nucleotide 

 residues were present either as mononucleotides or as terminal residues 

 carrying a monoesterified phosphoryl group in oligonucleotides consisting 

 otherwise solely of purine nucleotide residues. The same workers added 

 materially to this conclusion by periodate oxidation studies. Ribonucleic 

 acid and the products of its digestion with ribonuclease were stable to 

 periodic acid, but after treating the digest with phosphomonesterase, a 

 large periodate upta.ke -was observed which was equivalent to the amount 

 of inorganic phosphate liberated, and hence corresponded approximately 

 to the pyrimidine nucleotide content of the original nucleic acid. They also 

 showed that the larger, phosphorus-containing, fragments in the phos- 

 phomonoesterase-treated digests, i.e., oligonucleotides containing a termi- 

 nal pyrimidine residue, were also susceptible to periodate oxidation. Since 

 oxidation of nucleotides by periodate depends on the presence of unsubsti- 

 tuted hydroxyl groups at both C2' and C3. ,^''* they concluded that the 

 terminal (pyrimidine) residue in these oligonucleotides was linked to the 

 rest of the molecule through a position other than C2' or C3' . Claims that 

 ribonucleic acids themselves, and ribonuclease digests before phosphomono- 

 esterase treatment, reduce periodate'^- '"^ and lead tetraacetate'^^ have been 

 denied in more recent publications.^®'"- Periodate uptake after phospho- 

 rs C. E. Carter and W. E. Cohn, /. Am. Chern. Soc. 72, 2604 (1950). 

 lo" G. Schmidt, R. Cubiles, and S. J. Thannhauser, J. Cellular Comp. Physiol. 38, 



Suppl. 1,61 (1951). 

 i"' H. S. Loring and F. H. Carpenter, J. Biol. Chem. 150, 381 (1943). 

 i"" G. Schmidt, R. Cubiles, N. Zollner, L. Hecht, N. Strickler, K. Seraidarian, M. 



Seraidarian, and S. J. Thannhauser, J . Biol. Chem. 192, 715 (1951). 

 '" cf. W. Jones, J. Biol. Chem. 24, iii (1916). 

 i»* B. Lythgoe and A. R. Todd, J. Chem. Soc. 1944, 592. 

 los F. W. Allen, Federation Proc. 10, 155 (1951). 

 i"* R. A. Becher and F. W. Allen, J. Biol. Chem. 195, 429 (1952). 



