Assimilation of sulphur into the cell-wall polysaccharide of the red microalga Porphyridium sp. (Rhodophyta)

Marina Keidan, Hadas Broshy, Dorit Van Moppes, Shoshana Arad

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

The cell walls of red algae contain sulphated polysaccharides. It is believed that the bioactivity of such natural sulphated polysaccharides may be attributed to the sulphate groups. Knowledge of the mode of sulphation of these polysaccharides is, however, very limited. The current study forms part of our efforts to elucidate the mode of sulphation of the cell-wall polysaccharide of the red microalga Porphyridium sp. Although this microalga is an obligatory photoautotroph, under conditions of sulphate starvation it can assimilate the sulphur-containing amino acid cysteine (but not methionine) and incorporate sulphur from [35S]cysteine into the cell-wall polysaccharide. The ratio between 35S uptake to the soluble polysaccharide complex and to the cells was threefold higher from [35S]cysteine than that from Na235SO4, although the uptake of 35S to the cells was higher when Na235SO4 was used as the sulphur source. Pulse-chase experiments demonstrated that differences in the incorporation of 35S from the two sulphur sources were greater for the soluble polysaccharide complex (45.1% from [35S]cysteine vs. 13.9% from Na235SO4) than for the cellular fractions (bound polysaccharide, protein and low-molecular-weight fraction). SDS-PAGE analysis showed that the 35S label resided predominantly in the polysaccharide of the soluble complex and not in the glycoprotein. The effect of sodium chlorate, a sulphation inhibitor, on 35S incorporation into the soluble polysaccharide complex and the different cellular fractions depended on the 35S source: significant inhibition of sulphation of the soluble polysaccharide complex was found for [ 35S]cysteine as the source of sulphate, i.e. 87% vs. 36.4% for Na235SO4. This study suggests that in addition to the commonly accepted sulphate pathway, there is another sulphation pathway in which cysteine serves as the sulphur source.

Original languageEnglish
Pages (from-to)505-511
Number of pages7
JournalPhycologia
Volume45
Issue number5
DOIs
StatePublished - 1 Sep 2006

Keywords

  • Porphyridium sp.
  • Red microalga
  • Sodium chlorate
  • Sulphated polysaccharide
  • Sulphur assimilation pathways

ASJC Scopus subject areas

  • Aquatic Science
  • Plant Science

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