Structure of Agar from Gracilaria Spp (Rhodophyta) Collected in the People's Republic of China

Abstract

The structure of agars obtained from Gracilaria verrucosa, G. tenuistipitata, G. blodgettii, and G. eucheumoides collected in the People's Republic of China was determined. The agars consisted of charged agarose molecules that were eluted from DEAE-Sephadex A 50 with 0.5 Μ and 1.0 Μ Nad. The yield of agar from DEAE-Sephadex was increased to 80% after a treatment with 6.0 Μ urea, with the recovery of agarose molecules having a low charge density. Analysis by 13 C MNR spectroscopy showed L-gaIactose-6-sulfate as a minor constituent in the repeat units of agarose from G. verrucosa, G. tenuistipitata, and G. blodgettii. However, the NMR procedure was not sufficiently sensitive to detect other sugars contributing to the charge density of agarose molecules. Substitution of hydroxyl groups with methoxyl was detected by I3 C NMR spectroscopy; 6-O-methyl-D-galactose was present as a minor sugar in agarose from G. verrucosa and G. tenuistipitata, and 2-0-methyl-3,6-anhydro-L-galactose as a major sugar in agarose from G. eucheumoides.Agars from gametophytes and tetrasphorophytes of G. verrucosa yielded similar fractionation patterns on DEAE-Sephadex. Differences were noted in the fractionation pattern and 6-O-methyl-D-galactose content of agars from G. verrucosa collected from North and South China, possibly arising from a combination of different biological factors.

Agar from two coexisting species of Gracilaria (Gracilariaceae) from the Mexican Caribbean

“…Hoyle (1978) did not find differences in the yield or in the gel strength of the agar from male, female and tetrasporic plants of Gracilaria bursapastoris (Gmelin) Silva and G. coronopifolia J. Agardh (names as in the original paper). Similar findings were reported by Yao et al (1984) and Minghou et al (1985) for tetrasporic vs cystocarpic plants of G. verrucosa (Hudson) Papenfuss, and by Durairatnam and Nascimento (1985) for Gelidiopsis sjoestedtii Kylin. Neither Yao et al (1984) nor Minghou et al (1985) reported major differences in 3,6-anhydrogalactose and sulfate contents of the agar extracted from reproductive phases of Gracilaria species.…”

Seasonal changes in the chemical and gelling characteristics of agar from Gracilaria verrucosa collected in Turkey

“…Agar is known to be a mixture of molecules having a structure of the idealized agarose molecules and partially modified agarose substituted by sulfate, methoxyl and 4,6-0-(1-carboxyethylidene)-D-galactose at various positions (Araki, 1966;. The chemical heterogeneity of agar has been determined using anion exchange chromatography, sequential solvent extraction, 3 C -NMR and IR spectrophotometry (Minghou et al, 1985(Minghou et al, , 1988Yang & Liu, 1988;Truong et al, 1988;Lahaye et al, 1986;.…”

Use of solid and gel state 13C NMR spectroscopy for differentiation between agarophytes and carrageenophytes

“…All extracts were run at 77 'C, at which temperature they still would have been in the gel state ; however, the sharpness of the signals is comparable with those obtained at 90 ° C (Nicholaisen et al, 1980b) . The gel state spectrum of agarDB shows one minor peak at 58 .9 ppm due to the methyl carbon on a 6-0-methylated galactose residue, and another two at 71 .6 ppm and 73 .4 ppm, due to G-6 and G-5 carbons, respectively, of the methylated residue (Minghou et al, 1985). The peak at 69.2 ppm due to G-4 carbon of the same residue also was discernible .…”

“…The peak at 69.2 ppm due to G-4 carbon of the same residue also was discernible . In the Sigma agarose spectrum, a slight peak at 59 .0 ppm for methoxyl carbon was discernible, as well as two very minor peaks at 78 .7 and 78 .3 ppm, possibly due to carbons of anhydrogalactose residues methylated in the 2 position (Minghou et al ., 1985) . The agar extracted from E112 (Pterocladia capillacea), I although crude, has a spectrum that shows virtually no substitution .…”