Interactions of Ca(2+) with sphingomyelin and dihydrosphingomyelin.
The changes induced by Ca(2+) on human lens sphingolipids, sphingomyelin (SM), and dihydrosphingomyelin were investigated by infrared spectroscopy. Ca(2+)-concentration-dependent studies of the head group region revealed that, for both sphingolipids, Ca(2+) partially dehydrates some of the phosphate groups and binds to others. Ca(2+) affects the interface of each sphingolipid differently. In SM, Ca(2+) 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 Ca(2+) to carbonyl groups and/or strong tightening of interlipid H-bonds to levels beyond those in dehydrated samples of SM only. In contrast, Ca(2+) 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 Ca(2+) increases the transition temperature T(m) from 31.6 +/- 1.0 degrees C to 35.7 +/- 1.1 degrees C for SM and from 45.5 +/- 1.1 degrees C to 48.2 +/- 1.0 degrees C for dihydrosphingomyelin. Binding of Ca(2+) to some phosphate groups remains above T(m). The strength of the interaction is, however, weaker. This allows for the partial rehydration of these moieties. Similarly, above T(m), Ca(2+)-lipid and/or direct inter-lipid interactions are weakened and lead to the rehydration of amide groups.
Rujoi
Madalina
M
Department of Chemistry, University of Louisville, Louisville, Kentucky 40208, USA.
Borchman
Douglas
D
DuPré
Donald B
DB
Yappert
M Cecilia
MC
D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007908:Lens, Crystalline / Q000378:metabolism; D015394:Molecular Structure; D017550:Spectroscopy, Fourier Transform Infrared; D013109:Sphingomyelins / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
D013109:Sphingomyelins; D002118:Calcium