The galactan sulphate of the red alga Polysiphonia lanosa.

The structure of the galactan sulphate of P. lanosa has been established by a combination of methylation, treatment with alkali, and partial methanolysis of the alkali-treated polysaccharide to give derivatives of agarobiose. The polysaccharide belongs to the agar class, in which 3-linked derivatives of beta-D-galactose alternate with 4-linked derivatives of alpha-L-galactose in a repeating sequence. In addition to D-galactose itself, the 3-linked units include 6-O-methyl-D-galactose, D-galactose 6-sulphate, and a hitherto unreported unit, 6-O-methyl-D-galactose 4-sulphate. The 4-linked units include L-galactose 6-sulphate, 2-O-methyl-L-galactose 6-sulphate, and 3,6-anhydro-L-galactose.     

The structure of a galactan sulfate from the red seaweed Bostrychia montagnei

The sulfated, methylated galactan isolated from the red seaweed Bostrychia montagnei, showed an unusually narrow structural dispersion. This agaran has the defining linear backbone of alternating 3-linked beta-D-galactopyranosyl units and 4-linked alpha-L-galactopyranosyl and 3,6-anhydrogalactopyranosyl residues. The D-units have C-6 methylation, C-6 single stubs of xylopyranosyl and minor to trace amounts of (possible) C-6 linked single stubs of galactopyranosyl. These units are mainly sulfated on C-4 with lesser sulfation at C-6 and minor at C-2. The L-residues are mainly methylated on C-2 of the 3,6-anhydrogalactopyranosyl and sulfated on C-3 of the L-galactopyranosyl; minor amounts of 2,3- and 3,6-disulfated and 2-O-methyl or 2-O-glycosyl 3-sulfated L-galactopyranosyl were also found.     

The agar-type polysaccharide from the red alga Ceramium rubrum

Aqueous extraction of the red alga C. rubrum gave a galactan sulphate and, possibly, a separate glucan and xylan. The galactan sulphate has an alternating structure of the agar-type with D-galactose or 6-O-methyl-D-galactose as one alternating unit, and L-galactose, 3,6-anhydro-L-galactose; and their respective 2-methyl ethers as the other unit. Sulphate hemi-ester groups are present on position 6 of both D- and L-galactose residues, with smaller amounts on positions 2 and 4 of, probably, D-galactose residues. The polysaccharide differs from others previously examined in that most of the L-galactose residues are non-sulphated.     

Peroxidase from the red alga Cystoclonium purpureum

A particulate peroxidase has been extracted from the marine red alga Cystoclonium parpureum. Solubilisation was achieved by the use of either digit     

Sesquiterpenes from the marine red alga Laurencia distichophylla

A new cuparene-type sesquiterpene, isolaurenisol, has been isolated and identified from the New Zealand red alga Laurencia distichophylla. Major differences in the chemical composition of two morphologically indistinguishable samples of L. distichophylla are noted.     

Antiplasmodial halogenated monoterpenes from the marine red alga Plocamium cornutum

In our continuing search for antimalarial leads from South African marine organisms we have examined the antiplasmodial organic extracts of the endemic marine red alga Plocamium cornutum (Turner) Harvey. Two new and three known halogenated monoterpenes were isolated and their structures determined by standard spectroscopic techniques. The 3,7-dimethyl-3,4-dichloro-octa-1,5,7-triene skeleton is common to all five compounds. Interestingly, compounds bearing the 7-dichloromethyl substituent showed significantly higher antiplasmodial activity toward a chloroquine sensitive strain of Plasmodium falciparum.     

Mucilage from a fresh-water red alga of the genus Batrachospermum

The gelatinous polysaccharides of a Batrachospermum species have been extracted from the alga. The major polysaccharide is acidic and has been separated from neutral polysaccharides by chromatography on DEAE-cellulose. The constituent sugars of the acidic polysaccharide include d- and l-galactose, d-mannose, d-xylose, l-rhamnose, d-glucuronic acid, and two O-methyl sugars, which have been characterized as 3-O-methyl-l-rhamnose (l-acofriose and 3-O-methyl-d-galactose. Partial acid hydrolysis of this polysaccharide has given a complex mixture of neutral and acidic oligosaccharides. The two preponderant acidic oligosaccharides contained galactose and glucuronic acid in 1:1 ratio, suggesting the presence of a repeating sequence of these two residues as a major structural feature of the polysaccharide.     

Halogen chemistry of the red alga Asparagopsis

Ethanol extraction of fresh Asparagopsis taxiformis and A. armata, followed by pentane partition, results in the isolation of a series of halomethanes, among them MeI, CHCl₃, and CCl₄. Under these extraction conditions, esterification readily occurs, allowing the isolation and identification of a series of polyhaloethyl acetates and acrylates. The recognition of acetone and polyhaloacetones in these extracts suggests biological halogenations occur which result in haloform reactions.     

Sterols of the red alga Rissoella verruculosa

The Mediterranean red alga Rissoella verruculosa contains desmosterol in the esterified form whereas this sterol is not present in the free state.     

A sulfated galactan from the mucilaginous sheath of the red filamentous alga Chroodactylon ornatum (Stylonematophyceae,Rhodophyta)

The pseudofilamentous red alga Chroodactylon ornatum was grown in f/2 culture medium with the addition of 10, 34, and 100 μM (nominal concentration) cupric sulfate. The bioassays were terminated at two selected end points (days 4 and 12). Growth inhibition, changes in pigment composition, and oxidative stress indicators such as phenolic compounds and lipid peroxidation (dosed as thiobarbituric reactive substances) were observed in cultures with 34 and 100-μM cupric sulfate. Quinacrine (Atebrin) and chlorotetracycline fluorochromes showed abundant vacuoles of acidic content, related with mucilage secretion. Structural analyses by methylation, desulfation-methylation, alkaline treatment, and NMR spectroscopy revealed that the mucilaginous sheath of C. ornatum contains a sulfated galactan with a backbone of alternating 3-linked β-d-galactopyranose and 4-linked α-l-galactopyranose moieties, i.e., an agaran. The absence of 3,6-anhydrogalactose and of its precursor unit (α-galactose 6-sulfate) were confirmed. The highly sulfated polysaccharide contained these ester groups on the C-2 and C-4 hydroxyl groups of the 3-linked unit and on C-3 of the 4-linked units. The large proportion of sulfate esterification in this polysaccharide can be related to the extracellular biosorption of copper divalent cation (2.5?±?0.4 mg per gram of dry weight) and to copper tolerance in bioassays.     

Halogen chemistry of the red alga Bonnemaisonia

Complete accounts of the natural products chemistry of Bonnemaisonia nootkana, B. asparagoides, B. hamifera and Trailliella intricata are described. In contrast to the chemistry of the closely related alga Asparagopsis, Bonnemaisonia spp. do not produce halomethanes, but instead an array of C₇-C₉ halogen-containing ketones, alcohols and carboxylic acids. Biomimetic syntheses of these compounds suggest they are precursors and products of in vivo Favorsky rearrangements.     

Halogenated monoterpenes of the red alga Microcladia

The red marine algae Microcladia borealis, M. californica and M. coulteri produce several unusual halogenated monoterpenes including violacene, plocamene-B, plocamene-C, and plocamane-D. The isolation of these terpenes along with a study of their variation in each Microcladia at different locations are described.     

Bromo-compounds of the red alga Lenormandia prolifera

Six bromo-compounds and one bromo-chloro-compound have been detected in Lenormandia prolifera (C.Ag.) J. Agardh (Amansieae; Rhodomelaceae). Hydrolysis of the red pigment floridorubin from the same alga yielded five bromo-, one bromo-chloro and one chloro-phenol. The two main phenols of floridorubin were 2,3-dibromo-4,5-dihydroxy benzyl alcohol (lanosol) and 3,5-dibromo-p-hydroxybenzyl alcohol.     

Structure of a highly pyruvylated galactan sulfate from the Pacific green alga Codium yezoense (Bryopsidales, Chlorophyta)

A polysaccharide fraction consisting of d-galactose, sulfate, and pyruvate in a molar proportion of 4:2:1 was isolated from the green seaweed Codium yezoense by water extraction followed by ion-exchange chromatography. To elucidate its structure, modified polysaccharides were prepared by desulfation, depyruvylation, and by total removal of non-carbohydrate substituents. Structures of the native polysaccharide and of the products of its chemical modifications were investigated by methylation analysis as well as by 1D and 2D (1)H and (13)C NMR spectroscopy. The polysaccharide devoid of sulfate and pyruvate was subjected to two subsequent Smith degradations to afford a rather low-molecular and essentially linear (1-->3)-beta-d-galactan. A highly ramified structure was suggested for the native polysaccharide, which contains linear backbone segments of 3-linked beta-d-galactopyranose residues connected by (1-->6) linkages, about 40% of 3-linked residues being additionally substituted at C-6, probably by short oligosaccharide residues also containing (1-->3) and (1-->6) linkages. Sulfate groups were found mainly at C-4 and in minor amounts at C-6. Pyruvate was found to form mainly five-membered cyclic ketals with O-3 and O-4 of the non-reducing terminal galactose residues. The minor part of pyruvate forms six-membered cyclic ketals with O-4 and O-6. The absolute configurations of ketals (R for six-membered ketals and S for five-membered ones) were established using NMR spectral data.     

Genetic analysis of the Photosystem I subunits from the red alga, Galdieria sulphuraria

Currently, there are very little data available regarding the photosynthetic apparatus of red algae. We have analyzed the genes for Photosystem I in the recently sequenced genome of the red alga Galdieria sulphuraria. All subunits that are conserved between plants and cyanobacteria were unambiguously identified in the Galdieria genome: PsaA, PsaB, PsaC, PsaD, PsaE, PsaF, PsaI, PsaJ, PsaK and PsaL. From the plant specific subunits, PsaN and PsaO were identified but the sequence homology was much lower than for the subunits that are present in plants and cyanobacteria. The subunit PsaX, which is specific for thermophilic cyanobacteria, is not present in the Galdieria genome, whereas PsaM is a plastid-encoded protein as in other red algae. The sequences of the core subunits of PSI were further analyzed by mapping of the conserved areas in the crystal structures of cyanobacterial and plant PSI. The structural comparison shows that PSI from the red alga Galdieria may represent a common ancestral structure at the interface between cyanobacterial and plant PSI. Some subunits have a “zwitter” structure that contains structural elements that show similarities with either plant or cyanobacterial PSI. The structure of PsaL, which is responsible for the trimerization of PSI in cyanobacteria, lacks a short helix and the Ca²⁺ binding site, which are essential for trimer formation indicating that the Galdieria PSI is a monomer. However the sequence homology to plant PsaL is low and lacks strong conservation of the interaction sites with PsaH. Furthermore, the sites for interaction of plant PSI with the LHCI complex are not well conserved between plants and Galdieria, which may indicate that Galdieria may contain a PSI that is evolutionarily much more ancient than PSI from green algae, plants and the current cyanobacteria.     

Halogenated acetic and acrylic acids from the red alga Asparagopsis taxiformis

Nine halogenated acetic acids and nine halogenated acrylic acids have been identified in the aqueous extract of Hawaiian Asparagopsis taxiformis.     

Characterization of the edible red alga Meristotheca papulosa (Solieriaceae, Gigartinales) from Japan

The vegetative and reproductive morphology of the edible red alga Meristotheca papulosa (Montagne) J. Agardh (Solieriaceae) was reexamined based on material collected from various localities in Japan. Although the habit of the blades is variable according to the length and width of the axes, the frequency of branching and the abundance of proliferations, rbcL sequence analyses indicate their conspecificity. M. papulosa displays four distinctive reproductive features (presence of an auxiliary cell complex, occurrence of cystocarps on marginal proliferations and the blade surface (although very rare) in addition to the margins of axes, frequent production of spinose outgrowths on the pericarp and tetrasporangial initials typically basally attached to their parental cells) that have not been reported for M. papulosa from other areas. Although these features might warrant recognition of the Japanese entity as a separate species, a better understanding of their possible taxonomic value requires comparisons with M. papulosa from other geographic regions, including the type locality.     

Sulphate activation in the unicellular red alga Rhodella

ATP-sulphurylase (ATP: sulphate adenylyl-transferase, E.C. 2.7.74) from the unicellular red alga Rhodella has been purified 14-fold by (NH₄)₂SO₄ fractionation. It exhibits a temperature optimum of 31°, an activation energy of 10.8 kcal, has a pH optimum between 7.5 and 9.0 and forms unstable intermediates when incubated with ATP and group VI anions (CrO₄^2?, MoO₄^2?), WO₄^2?), resulting in the accumulation of pyrophosphate. Of the nucleotides tested, only ATP is acted upon by the enzyme. A divalent ion is required for activity and stimulation of the enzyme is 5 times higher with Mg²⁺ than any other ion tested. The actual substrate for the reaction is a Mg-ATP^2? complex. Free ATP inhibits the reaction. APS-[³⁵S] and traces of PAPS-[³⁵S] are formed when cell-free extract from Rhodella is incubated with ATP and sulphate-[³⁵S]. This indicates the existence of APS-kinase (ATP:adenylyl-sulphate 3¹-phosphotransferase, E.C. 2.7.1.25) as well as ATP-sulphurylase.