1H-NMR study on ganglioside amide protons: evidence that the deuterium exchange kinetics are affected by the preparation of samples.
The kinetics of H/2H chemical exchange of the amide proton has been suggested as one of the tools available for investigating hydrogenbond stabilizing interactions in gangliosides. The amide proton/deuterium (NH/2H) exchange rates in GM2 ganglioside were studied by 1H-NMR spectroscopy on 12 samples prepared following different procedures. In samples passed through a sodium salt Chelex-100 cation exchange resin column prior to being analysed the N-acetylneuraminic acid NH exchange occurred in less than 10 min and that of ceramide NH in 30 min. The N-acetylgalactosamine acetamido NH exchange was slower, the half-life of the signal ranging from 15 min to 3.5 h. Contact of the Chelex-treated GM2 samples with water, through a dialysis process, modified the NH/2H exchange rate values, the N-acetylgalactosamine acetamido NH exchange becoming faster than that of ceramide NH and similar to that of N-acetylneuraminic acid NH. Our results indicate that the deuterium/proton exchange rate strongly depends on sample preparation (ion content and minor contaminants present in water). The three-dimensional model involving the N-acetylgalactosamine acetamido NH and the N-acetylneuraminic acid carboxyl group hydrogen-bonding, which is supported by experimental evidence, cannot be confirmed by NH-exchange measurement.
Brocca
P
P
Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
Acquotti
D
D
Sonnino
S
S
D000577:Amides / Q000737:chemistry*; D002240:Carbohydrate Sequence; D003903:Deuterium; D005678:G(M2) Ganglioside / Q000737:chemistry*; D006207:Half-Life; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D011522:Protons; D013048:Specimen Handling / Q000379:methods*
D000577:Amides; D011522:Protons; D005678:G(M2) Ganglioside; D003903:Deuterium