دانلود رایگان مقاله ترکیبات پلی ساکاریدی جلبک دریایی قرمز هیپنئا موسیفورمیس

abstract

Two polysaccharide fractions isolated from Hypnea musciformis after room temperature- and hot water extraction, soluble after KCl precipitation of the more abundant carrageenans, were subfractionated by ion-exchange chromatography eluting with increasing concentrations of NaCl. The lowest NaCl concentration (0.2 M) eluted agarans. The dl-hybrids (or mixtures) eluted at intermediate concentrations of NaCl. The d/l-galactose ratio and the sulfate proportion increased with the NaCl concentration. Different types of substitution were present, mainly at C-3 with sulfate, Xyl and methylated Gal stubs, as well as low amounts of 3,6-AnGal. A novel constituent, identified as 3-C-carboxy-d-erythrose1 in its -furanosic form, was found linked to C-6 of -Gal units. A search carried outin other species like Iridaea undulosa and Kappaphycus alvarezii also revealed the same constituent. Finally, the late-eluting fractions were mostly carrageenans, with a structure consistent with that of a //-carrageenan hybrid. ©

4. Conclusion

So far, every time that a carrageenophyte was studied in detail, after separating the bulk of gelling carrageenans, a mixture of non-gelling polysaccharides was isolated. This mixture has always presented pure agarans, pure carrageenans, a glucan, and a group of different dl-hybrids ranging from those richer in agaran structures to those richer in carrageenan structures. As the mixed tetrasaccharide containing an -d- and an -l-Gal has never been isolated, there is a possibility that these so called hybrids do not exist (Ciancia & Cerezo, 2010), and that they are actually nonseparablemixtures. Hypnea musciformis isnot anexception.Besides the large amounts of -carrageenan produced by this seaweed (Cosenza et al., 2014), the 2 M KCl soluble fractions gather all the components of this mixture, with a great variety of sulfation locations, side stubs and structures. The most important feature, however, is the presence of 3-C-carboxy--d-erythrofuranosyl ((2R,3R)-apiofuranosyluronic acid) side stubs attached to O-6 of - d-galactose units in some fractions, and its positive identification in products from other seaweeds previously studied where, probably due to its low proportion and to its chromatographic overlapping, its presence was neglected. The existence of this side stub just in the so called hybrids opens new questions about its biosynthesis and about its role. Could they be markers of hybrid regions? Its discovery opens the door for further studies on the subject.