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Biophys J, June 2002, p. 3096-3104, Vol. 82, No. 6

Interactions of Ca2+ with Sphingomyelin and Dihydrosphingomyelin

Madalina Rujoi,* Douglas Borchman,dagger Donald B. DuPré,* and M. Cecilia Yappert*

 *Department of Chemistry and  dagger Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky 40208 USA

The changes induced by Ca2+ on human lens sphingolipids, sphingomyelin (SM), and dihydrosphingomyelin were investigated by infrared spectroscopy. Ca2+-concentration-dependent studies of the head group region revealed that, for both sphingolipids, Ca2+ partially dehydrates some of the phosphate groups and binds to others. Ca2+ affects the interface of each sphingolipid differently. In SM, Ca2+ shifts the amide I' band to frequencies lower than those in dehydrated samples of SM alone. This could be attributed to the direct binding of Ca2+ to carbonyl groups and/or strong tightening of interlipid H-bonds to levels beyond those in dehydrated samples of SM only. In contrast, Ca2+ induces relatively minor dehydration around the amide groups of dihydrosphingomyelin and a slight enhancement of direct lipid-lipid interactions. Temperature-dependent studies reveal that 0.2 M Ca2+ increases the transition temperature Tm from 31.6 ± 1.0°C to 35.7 ± 1.1°C for SM and from 45.5 ± 1.1°C to 48.2 ± 1.0°C for dihydrosphingomyelin. Binding of Ca2+ to some phosphate groups remains above Tm. The strength of the interaction is, however, weaker. This allows for the partial rehydration of these moieties. Similarly, above Tm, Ca2+-lipid and/or direct inter-lipid interactions are weakened and lead to the rehydration of amide groups.

Biophys J, June 2002, p. 3096-3104, Vol. 82, No. 6
© 2002 by the Biophysical Society   0006-3495/02/06/3096/09  $2.00


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