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Keywords:

  • agar biosynthesis;
  • agarophyte;
  • nudeoside diphosphate monosaccharides;
  • Pterocladia capillacea;
  • pohsaccharide;
  • Rhodophyta

ABSTRACT

The following nucleoside diphosphate monosaccharides (sugar nucleotides) were identified by HPLC from Pterocladia capillacea Born and Thur.: ADP-glucose, UDP-glucose, UDP-d-galactose, and GDP-glucose + mannose. GDP-l-galactose was not identified due to the lack of a standard. Several extraction methods were evaluated for their efficacy. A freeze/ thaw (liquid N2) step fallowed by formic acid (1 M) extraction, reduced pressure evaporation, and solubilization in water was the preferred method. Differences in media nitrate that resulted in different tissue-N levels (1.8, 2.3, and 3.5% dry wt) and agar yields (34, 31, and 28% dry wt, respectively) also resulted in a marked difference in UDP-d-galactose and ADP-glucose tissue levels (decrease with increasing tissue-N) while the levels of the other sugar nucleotide agar precursors remained unchanged. Activities of UDP-glucose, GDP-glucose, and GDP-mannose pyrophosphorylases, and UDP-D-glucose-4-epimerase were detected in cell-free extracts using unlabeled and 14C-labeled substrates. This study-strongly supports the proposition that the d-galactose component of agar is synthesized via G-1-P [RIGHTWARDS ARROW] UDP-glucose[RIGHTWARDS ARROW] UDP-d-galactose and that, the l-galactoae component is produced via mannose-1-P [RIGHTWARDS ARROW] GDP-mannose [RIGHTWARDS ARROW] GDP-l-galactose.