Interactions of Inorganic Phosphate and Sulfate Anions with Collagen
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- 作者：Edward L. Mertz and Sergey Leikin
- 刊名：Biochemistry
- 出版年：2004
- 出版时间：November 30, 2004
- 年：2004
- 卷：43
- 期：47
- 页码：14901 - 14912
- 全文大小：342K
- 年卷期：v.43,no.47(November 30, 2004)
- ISSN：1520-4995
文摘
We use direct infrared measurements to determine the number of binding sites, their dissociationconstants, and preferential interaction parameters for inorganic phosphate and sulfate anions in collagenfibrils from rat tail tendons. In contrast to previous reports of up to 150 bound phosphates per collagenmolecule, we find only 1-2 binding sites for sulfate and divalent phosphate under physiological conditionsand ~10 binding sites at low ionic strength. The corresponding dissociation constants depend on NaClconcentration and pH and vary from ~50 
M to ~1-5 mM in the physiological range of pH. In fibrils,bound anions appear to form salt bridges between positively charged amino acid residues within regionsof high excess positive charge. In solution, we found no evidence of appreciable sulfate or phosphatebinding to isolated collagen molecules. Although sulfate and divalent phosphate bind to fibrillar collagenat physiological concentrations, our X-ray diffraction and in vitro fibrillogenesis experiments suggestthat this binding plays little role in the formation, stability and structure of fibrils. In particular, wedemonstrate that the previously reported increase in the critical fibrillogenesis concentration of collagenis caused by preferential exclusion of "free" (not bound to specific sites) sulfate and divalent phosphatefrom interstitial water in fibrils rather than by anion binding. Contrary to divalent phosphate, monovalentphosphate does not bind to collagen. It is preferentially excluded from interstitial water in fibrils, but ithas no apparent effect on critical fibrillogenesis concentration at physiological NaCl and pH.
M to ~1-5 mM in the physiological range of pH. In fibrils,bound anions appear to form salt bridges between positively charged amino acid residues within regionsof high excess positive charge. In solution, we found no evidence of appreciable sulfate or phosphatebinding to isolated collagen molecules. Although sulfate and divalent phosphate bind to fibrillar collagenat physiological concentrations, our X-ray diffraction and in vitro fibrillogenesis experiments suggestthat this binding plays little role in the formation, stability and structure of fibrils. In particular, wedemonstrate that the previously reported increase in the critical fibrillogenesis concentration of collagenis caused by preferential exclusion of "free" (not bound to specific sites) sulfate and divalent phosphatefrom interstitial water in fibrils rather than by anion binding. Contrary to divalent phosphate, monovalentphosphate does not bind to collagen. It is preferentially excluded from interstitial water in fibrils, but ithas no apparent effect on critical fibrillogenesis concentration at physiological NaCl and pH.