Author
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Hunt, Curtiss |
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Submitted to: Book Chapter
Publication Type: Book / Chapter Publication Acceptance Date: 8/1/2002 Publication Date: 6/1/2002 Citation: Hunt, C.D. 2002. Boron-binding biomolecules: a key to understanding the beneficial physiologic effects of dietary boron from prokaryotes to humans. In: Goldbach, H.E., Rerkasem, B., Wimmer, M.A., Brown, P.H. Thellier, M., Bell, R.W., editors. Boron in Plant and Animal Nutrition. New York, NY:Kluwer Academic Publishers. p.21-36. Interpretive Summary: Although the biochemical mechanisms responsible for the physiologic effects of boron across the phylogenetic spectrum are poorly understood, the unique nature of boron biochemistry suggests specific lines of investigation. Biomolecules possessing vicinal cis-diols (VCD) or proximal hydroxyls in the correct orientation form boroesters with association constants that vary from weak to highly stable. The antibiotic boromycin has four centrally directed oxygens that provide an ideal geometry for accommodation of a boron atom and formation of a stable borodiester. Rhamnogalacturonan RG)-IIs dimers in pectin fractions of higher plants are cross-linked by a borodiester. The cross-links in RG-II may be "load-bearing," acid-labile linkages that are hydrolyzed by a decrease in wall pH during auxin-induced cell expansion. All NAD+-, NADP-, or FAD-requiring oxidoreductase enzymes are competitively inhibited by borate in vitro (~0.4 mM) because boron forms boroesters with the VCD-containing ribose residues of these co- factors. Diadenosine phosphates (cell signal nucleotides) with four or more phosphates have high boron binding affinities apparently through cooperative chelation of boron between opposed riboses. Boron reduces hemostasis and may form a boron adduct with serine proteases in the coagulation cascade that mimics the adduct formed during normal substrate hydrolysis. The biochemical mechanisms responsible for the effect of boron observed in many physiological systems may include stabilization of specific reactive compounds and signal suppression to down-regulate specific enzymatic activities including those typically elevated during inflammation. Technical Abstract: Although the biochemical mechanisms responsible for the physiologic effects of boron across the phylogenetic spectrum are poorly understood, the unique nature of boron biochemistry suggests specific lines of investigation. Biomolecules possessing vicinal cis-diols (VCD) or proximal hydroxyls in the correct orientation form boroesters with association constants that vary from weak to highly stable. The antibiotic boromycin has four centrally directed oxygens that provide an ideal geometry for accommodation of a boron atom and formation of a stable borodiester. Rhamnogalacturonan RG)-IIs dimers in pectin fractions of higher plants are cross-linked by a borodiester. The cross-links in RG-II may be "load-bearing," acid-labile linkages that are hydrolyzed by a decrease in wall pH during auxin-induced cell expansion. All NAD+-, NADP-, or FAD-requiring oxidoreductase enzymes are competitively inhibited by borate in vitro (~0.4 mM) because boron forms boroesters with the VCD-containing ribose residues of these co- factors. Diadenosine phosphates (cell signal nucleotides) with four or more phosphates have high boron binding affinities apparently through cooperative chelation of boron between opposed riboses. Boron reduces hemostasis and may form a boron adduct with serine proteases in the coagulation cascade that mimics the adduct formed during normal substrate hydrolysis. The biochemical mechanisms responsible for the effect of boron observed in many physiological systems may include stabilization of specific reactive compounds and signal suppression to down-regulate specific enzymatic activities including those typically elevated during inflammation. |
