Journal of Lipid Research, Vol 32, 621-627, Copyright © 1991 by Lipid Research, Inc.
Calcium binding by monosulfate esters of taurochenodeoxycholate
RD Stevens, L Lack and PG Killenberg
Department of Medicine, Duke University Medical Center, Durham, NC 27710.
The effect of sulfate esterification of the 3 alpha- or 7 alpha- hydroxyl
groups of taurochenodeoxycholate on calcium binding was studied at 0.154 M
NaCl in the presence and absence of phosphatidylcholine using a calcium
electrode. For comparison, similar studies were made with
taurochenodeoxycholate, taurodeoxycholate, and taurocholate. No high
affinity calcium binding was demonstrable for any of these bile salts in
pre-micellar solutions. Taurine-conjugated bile salts have greater affinity
for calcium when in a micellar form. At elevated bile salt concentrations,
the calcium binding of unsulfated dihydroxy taurine conjugates was similar
to that of the monosulfate esters of taurochenodeoxycholate. The presence
of phosphatidylcholine decreased calcium binding of the unsulfated
dihydroxy bile salts and slightly increased calcium binding by
taurocholate. However, the addition of phosphatidylcholine to monosulfate
esters of taurochenodeoxycholate results in large increments in calcium
binding. The results indicate that increased calcium binding due to the
presence of phosphatidylcholine in bile salt solutions depends, in part, on
the hydrophilicity of the bile salt and that the interaction of monosulfate
esters of taurochenodeoxycholate with phosphatidylcholine leads to the
formation of a high affinity calcium binding site.
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