Carrageenans from the tetrasporic stages of Gigartina clavifera and Gigartina alveata (Gigartinaceae, Rhodophyta).

Modern chemical and spectroscopic techniques have been used to characterise the polysaccharides extracted from the tetrasporic life stages of Gigartina clavifera and Gigartina alveata. Both are predominantly xi-carrageenans. About one in six of the 3-linked residues in both polysaccharides also have a pyruvate acetal group at the 4- and 6-positions. In addition, a similar proportion of the 4-linked units of each polysaccharide are devoid of sulfate groups, whilst more have sulfate esters on both O-2 and O-6. Some of the 3-linked units contain a sulfate at the 6-position in addition to that at O-2. The polysaccharide from tetrasporophytic G. alveata also contains a small but significant number of 3,6-anhydrogalactosyl units, most of which are naturally sulfated at the 2-position.