Properties of astaxanthin/Ca2+ complex formation in the deceleration of cis/trans isomerization.

Deceleration of the regioselective cis/trans isomerization of all-trans-astaxanthin (ASTX) in the presence of Ca2+ was shown by HPLC analysis. The NMR and ITC analyses provided evidence for complexation of ASTX with Ca2+ in 1:2 stoichiometry via chelation at both carbonyl and hydroxyl groups. The rotation across torsion omega6 (C5-C6-C7-C8) upon complexation is consistent with the NOE between 7-H and 5-CH3. This study supports the inhibitory effect of ASTX on calcium-induced turbidity of lens crystallins.