On-Line Liquid Chromatography Electrospray lonization Mass Spectrometry for the Characterization of kappa- and iota-Carrageenans.Application to the Hybrid iota-u-Carrageenans

摘要

An on-line liquid chromatography electrospray ionization mass spectrometty (MS) method was developed for the characterization of polymers of kappa- (extracted from Kap-paphycus alvarezii),iota-,and hybrid iota-u-carrageenans (both extracted from Eucheuma denticulatum) enzy-matically digested with specific carrageenase enzymes.Applying either CID MS/MS or in-source fragmentation mechanisms,the results demonstrated that none of the polymers of kappa- or iota-carrageenans existed with their ideal repeating units.On the polymer of kappa-carrageenan,the nonideal structures identified consisted of iota-neocarrabiose sulfate units.On the polymer of iota-carrageenan,the non-ideal structures identified consisted of the following:(i) kappa-neocarrabiose sulfate units,(ii) iota-neocarrabiose sulfate units with an additional sulfate group,and (iii) t-neocar-rabiose sulfate units with an additional sulfate and a pyruvate acetal group.For both kappa- and iota-carrageenans,the nonideal structures were randomly distributed on the polymers.The method was then applied for the characterization of a hybrid polymer of iota-u-carrageenans,enzy-matically digested with iota-carrageenase.The results did not reveal an ideal oligosaccharide of nu-carrageenan,suggesting that the iota-carrageenase enzyme could cleave only reduced "densities" of nu-carrageenan repeating units.In addition,information about the sequence of hybrid iota-u-carrageenans from E.denticulatum is deduced.