Calcium effects on self association of bile salts (BS) evaluated by solubilization of lipophilic orange-OT

Vecchio, S. Del; Ostrow, J. Donald

doi:10.1016/0168-8278(91)91084-t

“…The Ca2 + -associated increase in GC and TCDC binding was accompanied by a large rise in the binding of "premicellar" aggregates, and all of the increase in TCDC binding was accounted for by the enhanced premicellar component. Although it has been suggested that Ca2+ can influence the aggregation of bile salts (311, our results did not show any substantial effect, and this is in agreement with previous observations (22,32). Because Ca2+ did not affect aggregation, the increased bile salt binding must be caused principally by excess Ca2+ binding to the HAP surface.…”

Section: Discussionsupporting

confidence: 91%

“…The main effect of Ca2 + was to cause the fluorescence to remain constant at GCDC concentrations greater than 6 mmoVL. This effect was associated with the formation of very viscous solutions and has also been observed by others (22). Because Ca2 + had no major effect on bile salt aggregation, it seemed probable that Ca2 + increased the binding of susceptible bile salts by altering the nature of the HAP surface.…”

Section: Ftir Determination Of Gcdc Binding To Acp Andsupporting

confidence: 77%

Interaction of bile salts with calcium hydroxyapatite: Inhibitors of apatite formation exhibit high-affinity premicellar binding,

Qiu¹

1992

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Of the major human bile salts, only the glycine-conjugated dihydroxy species prevent the transformation of amorphous calcium phosphate to calcium hydroxyapatite, a component of gallstones; we have proposed that this inhibition occurs by competition between the bile salt and HPO4(2-) anions for binding site on the apatite crystal embryo. Now we show that the binding affinity of bile salts to fully mature hydroxyapatite has the following order: glycine-conjugated dihydroxy salts > taurine-conjugated dihydroxy salts > glycocholate approximately taurocholate. Glycine-conjugated dihydroxy bile salts bound with high affinity as "premicellar" aggregates, but the remaining species appeared to bind as a wider range of aggregate sizes. Glycochenodeoxycholate binding was decreased as the pH increased from 6.6 to 9.8 and the apatite surface charge reversed from net positive to net negative. Binding was competitively inhibited by HPO4(2-), but not by H2PO4-. Ca2+ promoted the binding of glycochenodeoxycholate, taurochenodeoxycholate and glycocholate, and for the latter two bile salts the increase was associated with enhanced "premicellar" binding. The binding of taurocholate was not influenced by Ca2+. When either glycocholate or taurocholate was mixed with glycochenodeoxycholate, mixed aggregates were formed that had a lower affinity for apatite than had pure glycochenodeoxycholate aggregates. Because only glycine-conjugated dihydroxy bile salts inhibit apatite formation, these results suggest that inhibition depends on high-affinity "premicellar" bile salt-apatite binding.

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Interaction of Bile Salts With Calcium Hydroxyapatite: Inhibitors of Apatite Formation Exhibit High-Affinity Premicellar Binding

Qiu

¹

,

Soloway

²

,

Crowther

³

1992

Hepatology

3

0

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Of the major human bile salts, only the glycine-conjugated dihydroxy species prevent the transformation of amorphous calcium phosphate to calcium hydroxyapatite, a component of gallstones; we have proposed that this inhibition occurs by competition between the bile salt and HPO4(2-) anions for binding site on the apatite crystal embryo. Now we show that the binding affinity of bile salts to fully mature hydroxyapatite has the following order: glycine-conjugated dihydroxy salts > taurine-conjugated dihydroxy salts > glycocholate approximately taurocholate. Glycine-conjugated dihydroxy bile salts bound with high affinity as "premicellar" aggregates, but the remaining species appeared to bind as a wider range of aggregate sizes. Glycochenodeoxycholate binding was decreased as the pH increased from 6.6 to 9.8 and the apatite surface charge reversed from net positive to net negative. Binding was competitively inhibited by HPO4(2-), but not by H2PO4-. Ca2+ promoted the binding of glycochenodeoxycholate, taurochenodeoxycholate and glycocholate, and for the latter two bile salts the increase was associated with enhanced "premicellar" binding. The binding of taurocholate was not influenced by Ca2+. When either glycocholate or taurocholate was mixed with glycochenodeoxycholate, mixed aggregates were formed that had a lower affinity for apatite than had pure glycochenodeoxycholate aggregates. Because only glycine-conjugated dihydroxy bile salts inhibit apatite formation, these results suggest that inhibition depends on high-affinity "premicellar" bile salt-apatite binding.

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Inhibition of calcium phosphate precipitation by bile salts: a test of the Ca(2+)-buffering hypothesis.

Crowther¹,

Okido²

1994

Journal of Lipid Research

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Calcium effects on self association of bile salts (BS) evaluated by solubilization of lipophilic orange-OT

Cited by 3 publications

References 0 publications

Interaction of bile salts with calcium hydroxyapatite: Inhibitors of apatite formation exhibit high-affinity premicellar binding,

Interaction of bile salts with calcium hydroxyapatite: Inhibitors of apatite formation exhibit high-affinity premicellar binding,

Interaction of Bile Salts With Calcium Hydroxyapatite: Inhibitors of Apatite Formation Exhibit High-Affinity Premicellar Binding

Inhibition of calcium phosphate precipitation by bile salts: a test of the Ca(2+)-buffering hypothesis.

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