title: The system of sulfated galactans from the red seaweed Gymnogongrus torulosus (Phyllophoraceae, Rhodophyta): Location and structural analysis.
abstract: Sulfated polysaccharides were localized in the cuticle, cortex and medulla of the gametophyte thallus, being more concentrated in the intercellular matrix than in the cell walls. During the water extraction sequence, a small percentage of galactan sulfates (5.1% of dry seaweed) with average low Mr (6-11.4kDa) were extracted at room temperature without disturbing the cellular arrangement, while sulfated galactans of average medium Mr (18-45kDa) were obtained by further hot-water extractions (52.4% of dry seaweed), with diorganization of the tissue. The residue (40.0% of dry seaweed) still contained carrageenan-type (major) and agaran-type (minor) galactans. Part of these galactans was extracted with 8.4% LiCl solution in DMSO, from which "pure" κ/ι-carrageenans were isolated. Carrageenans and agarans were extracted in a ratio 1:0.5, showing the highest amount of agaran-structures for a carrageenophyte. The galactans comprise alternating 4-sulfated (major) and non-sulfated (minor) 3-linked β-d-galactopyranose units, and 4-linked α-galactopyranose units with the following substitutions: (i) non-sulfated and 2-sulfated 3,6-anhydro-α-d-galactopyranose residues in the carrageenan-structures, which belong to the κ-family (κ/ι-carrageenans); (ii) 3-sulfated α-l-galactopyranose units and 2-sulfated 3,6-anhydro-α-l-galactopyranose residues in the agaran-structures. Alkaline treatment and alkaline dialysis of the main extracts gave "pure" κ/ι-carrageenans, showing that carrageenan molecules are extracted together with low Mr agarans or agaran-dl-hybrids.
authors.affiliation: Departamento de Química Orgánica (CIHIDECAR-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria - Pabellón 2, 1428 Buenos Aires, Argentina.
authors.forename: José M
authors.initials: JM
authors.lastname: Estevez
authors.affiliation: Cátedra de Química Orgánica, Departamento de Biología Aplicada y Alimentos (CIHIDECAR-CONICET), Facultad de Agronomía, Universidad de Buenos Aires, Avda. San Martín 4453, 1417 Buenos Aires, Argentina.
authors.forename: Marina
authors.initials: M
authors.lastname: Ciancia
authors.affiliation: Departamento de Química Orgánica (CIHIDECAR-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria - Pabellón 2, 1428 Buenos Aires, Argentina. Electronic address: cerezo@qo.fcen.uba.ar.
authors.forename: Alberto S
authors.initials: AS
authors.lastname: Cerezo
keywords: Agarans; Carrageenans; Cell wall; Gymnogongrus torulosus (Phyllophoraceae); Red seaweed; Sulfated galactans; l-Galactose