Diadenosine phosphates and S-adenosylmethionine:: novel boron binding biomolecules detected by capillary electrophoresis

There is evidence that boron has a physiological role in animals and humans, but the search for boron binding biomolecules has been difficult because useful radioactive boron isotopes do not exist. To overcome this limitation wt: used capillary electrophoresis to identify and quantify boron binding to biomolecules by detecting the negative charge boron imparts to ligands. The effect of molecular structure and proximal electronic charges of adenosine and molecules with adenosine moieties including S-adenosylmethionine (SAM) and diadenosine polyphosphates (Ap(n)A) were compared. The boron affinity of the test species varied with the rank order SAM- congruent to Ap(6)A congruent to Ap(5)A > Ap(4)A > Ap(3)A congruent to NAD(+) > Ap(2)A > NADH congruent to 5 ' ATP > 5 ' ADP > 5 ' AMP > adenosine > 3 ' AMP congruent to 2 ' AMP congruent to cAMP congruent to adenine. Test species with vicinal cis-diols bound boron: species without those moieties did not. Boron binding affinity increased when proximal cationic moieties were present. Anionic moieties remote from the cis-hydroxyl binding site also positively influenced boron binding affinity. In the Ap,,A species. cooperative complexing of boron between the terminal ribose moieties apparently occurred. In these species boron affinity rester than expected for two monocomplexes was observed and binding affinities increased as more phosphate groups (beyond three) were present separating the terminal moieties. Our results indicate that Ap(6)A. Ap(5)A, Ap(4)A, Ap(3)A, and SAM have higher affinities for boron than any other currently recognized boron ligand present in animal tissues including NAD(+). (C) 2001 Elsevier Science B.V. All rights reserved.