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 Agar is a complex mixture of polygalactans obtained from red algae, having a basic

disaccharide repeat unit: 3-O-(3,6-anhydro-L-galactopyranosyl-!-"-galactopyranose

#hich can be substituted #ith methyl ($-6 of "-unit, $-% of L-unit or #ith sulfate ($-6 og L-

unit& 'he neutral form of these polysaccharides is called agarose: $ommercial grade agar

and agarose are mainly obtained from Gelidium and Gracilaria species&

'he initial approach of our laboratory #as the development of thalli cultivation, agar

extraction and analytical procedures oriented to the production and the study of agarose&

ince then several other forms have been observed for these polymers, as earlier studies

predicted (), especially #hen their distribution #ithin main axis and lateral branches #ere

ta*en into consideration&

+n order to verify the hypothesis that all these polymers reflect different steps of agar

metabolism (%, it #as necessary to revie# the methodology of structural investigations

and studies of their heterogeneity& +n this #or*, special attention #as given to the

substituents of "-galactose units since this residue is not only the site of O-methylation at

the $-6 (6-O-methyl-L-galactose 6-O-e-gal (3&

.e have compared the #ater (/ and ethanol0#ater extractions and hace developed a ne#

extraction procedure (1igure ) #hich fractionates the polymers according to their degree

of substitution (sulfation, methylation&

ain axis (A and lateral branches (L! from Gracilaria verrucosa  #ere cultivated

separately under promoting and non-promoting gro#th conditions&

'he monosaccharide content of the polymers #as obtained by 2L$ analysis of their alditol

acetates (6& 'he sulfate content #as measured by and 4L$ method (5& 3,6-anhydro-galactose and total carbohydrate contents #ere estimated by colorimetric assays (,7&

'he evolution of the polymers #as monitored by comparison #ith the structural data of the

corresponding fractions obtained from native plants (table +& 'he degree of substitution of

the "-unit #as computed from the 6-O-methyl-gal and /-O-methyl contents&

 At the end of the cultivation cycle (% months, the only significant variation in the

composition of A, #as an increase of /-O-methyl-gal content gro#th-promoting

conditions as earlier described for 2racilaria ti*vahiae ()8, #hile L! represented a

remar*able increase in 6-O-methyl-gal& +t is interesting to note that the degree of

substitution (" remained the same in both cases& 9nder non-promoting conditions nosignificant variation #as observed, except a slight increase of 6-O-methyl-gal in L!&

!etter recovery #as obtained #ith the ethanol0#ater extraction, #here A #as the ma;or

fraction& 1or the #ater extraction, .! #as the main fraction (figure %& 'he yield of hot

soluble polysaccharides (A, !, .A and .! #as greater from L! than from A&

'he 6-O-e-gal0 /-O-e-gal ratio decreased during the extraction step, the lo#est value

being obtained for algal residues in all cases& An inverse relationship #as observed

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bet#een this ratio and the sulfate content (data not sho#n& As the /-O-e-gal content is

the highest for the algal residues, this sugar #as demonstrated to belong to neutral type

polysaccharides closely bound to the cell #all and thus having lo# extractability&

Our results have further allo# us to demonstrated the implication of /-O-methyl-galactose

in the agar metabolism and a continuous exchange bet#een O-methylation and /-O-

methyl-galactose lin*age to the "-galactose units during maturation of thalli ())-)7&

References

)& +<umi, =& )75%& $hemical heterogeneity of the agar from 2racilaria verrucosa& >&!iochem& >ap&, 5% (): )3?-)/8&

%& $hristiaen ", ' tadler, A Ondar<a @ $ erdus& )75& tructures and functions

of the polysaccharide from 

the cell #all ofGracilaria verrucosa

(Bhodophyceae,2igartinales& ydrobiologia )?)0)?%: )37-)/6&

3& =aramanos C, A Ondar<a, 1 !ellanger, " $hristiaen @ oreau& )77& 'helin*age of /-O-methyl Lgalactopyranose  in the agar polymers from Gracilaria

verrucosa. $arbohydrate Besearch )5: 73-)8)&

/& $hristiaen "& '&, =aramanos, C& , tadler, '& and & orvan& ()75& 1ractionspolysaccharidiDues extradites de la paroi de 2racilaria verrucosa& ci& de l Eau, 6,)%)-)3?&

?& Lahaye , $ Bochas @ . Caphe& )76& A ne# procedure for determining the

heterogeneity of agar polymers in the cell #alls of Gracilaria sp& (2racilariaceae,Bhodophyta& $an& >&!ot& 6/: ?57-??&

6& lone*er >& )75%& 2as-liDuid chromatography of alditol acetates& n: .histler BL@ >F !emiller& ethods in $arbohydrate $hemistry 6: %8-%/& Academic 4ress,Fe# Cor*&

5& aas, 1&&, offmann, +&, an armelen, && and L&& de =o*& )76&Befractometric determination of sulphate and other anions in plants separated by4L$& 4lant @ oil, 7): )%7-)3%&

& "ubois, &, 2illes, 1&A&, amilton, >&=&, Bebers, 4&A& and mith, 1& ()7?6&$olorimetric method for the determination of sugars and related substances& Anal&!iochem&, %, 3?8-3?6&

7& Caphe, .& )768& $olorimetric determination of 3,6-anhydroga- lactose andgGlactose in marine algal poloysaccharides& Anal& $hem& 3%: )3%5-)338&

)8& $raigie, >&&, and H&$& .en&)7/ ffects of temperature and tissue age on gelstrength and composition of agar from 2racilaria ti*vahiae (Bhodophyceae& $an&>& !ot& 6%:66?I)658&

))& =imon '& !ird& )778& vidence of /-O-methyl-J-L-galactose in the agar ofGracilaria verrucosa  strain 2-)6& )7, >ournal of Applied 4hycology  olume %, Fumber /, 33-3/&

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