Tomoyoshi Ikawa

Distribution of a 334 UV-Absorbing-Substance in Algae, with Special Regard of its Possible Physiological Roles

A survcy on the existence oia 334 nrn UV-absorbing substancc in algac H S been performcd for 2 species ot l he Cyunophyta,45 spccies of thc Rhodophyta, 13 species of the Phaeophyta and 10 species of the Chlorophyll Ι ΐ was tound that eithcr the substance seeming to bc this compound or similar compounds having absorption bands in closc proximity to it are existent in all algae tested, and that these UV-absorbing substances secm to have sornc physiological relationships with Chlorophylls and other pigments and ihe depth of the individual algat habitats.

Physiological Roles of a Substance 334 in Algae

Effects of light intensity, nitrogen and phosphorus nutrients on thc

Characterization of Salt-Regulated Mannitol-1-Phosphate Dehydrogenase in the Red Alga Caloglossa continua

Mannitol-1-phosphate (M1P) dehydrogenase (M1PDH; EC 1.1.1.17), an enzyme catalyzing the reduction of Fru-6-phosphate (F6P) to M1P in algal mannitol biosynthesis, was purified to homogeneity from a cell homogenate of the eulittoral red alga Caloglossa continua (Okamura) King et Puttock. The enzyme was a monomer with an apparent molecular mass of 53 kD, as determined by gel filtration and SDS-PAGE, and exhibited an pI of approximately 5.5. The substrate specificity was very high toward F6P and M1P for respective reductive and oxidative reactions. The enzyme was found to be a sulfhydryl-type, because its activity was inhibited by N-ethylmaleimide and p-hydroxymercuribenzoate, and the inhibition by p-hydroxymercuribenzoate was rescued by 2-mercaptoethanol. Some unknown factors in the extract may also have inhibited the activity, because the total activity was greatly increased through the purification procedure. The optimum pH for F6P reduction was changed from 6.0 or lower to 7.2 by the addition of 200 mm NaCl. The reduction of F6P showed strong substrate inhibition above 0.5 mm. However, Km(F6P) of M1PDH was increased eight times by the addition of 200 mm NaCl, whereas Vmax was in a similar range with the avoidance of substrate inhibition by F6P. These results indicate that the enzyme was finely and directly regulated by the salt concentration without the requirement for gene expression. M1PDH can therefore be a key enzyme for regulating mannitol biosynthesis when the alga is stressed by a salinity change.

Light-enhanced induction of ascorbate peroxidase in Japanese radish roots during postgerminative growth

Abstract During postgerminative growth of Japanese radish ( Raphanus sativus L. var. hortensis ) in continuous light, the specific activity of APX (EC 1.11.1.11) in roots markedly increased 2 days after imbibition. This increase in APX activity in roots was accompanied by increases in activities of the enzymes in the ascorbate-dependent H 2 O 2 -scavenging system, superoxide dismutase (EC 1.15.1.1), monodehydroascorbate reductase (EC 1.6.5.4), dehydroascorbate reductase (EC 1.8.5.1) and glutathione reductase (EC 1.6.4.2) which may participate in the detoxification of H 2 O 2 generated via the β-oxidation of fatty acid in seeds and consequent active cell division in the meristem/determination zone of the root. Catalase (EC 1.11.1.6) activity was not detected and guaiacol peroxidase (EC 1.11.1.7) activity was extremely low in roots at this stage of postgermination. A prominent increase in APX activity in roots under light conditions reflected the increases in protein level and mRNA accumulation of cytosolic APX. These results indicate that at the early stages of postgermination of Japanese radish, cytosolic APX is rapidly induced in growing roots and its induction may be regulated by light. The role of cytosolic APX in roots is discussed in relation to detoxification of H 2 O 2 generated in the process of postgerminative growth.

Alginate Lyase Activities in the Extracts from Several Brown Algae.

Crudc enzymc extracts were prepared from several brown algae, and incubated with C-alginatos, non-radioactivc alginates, short polymannuronide (SM) and -guluronide (SG), short mixed residue-polyuronide (SMG). The reuc t ion products positive to TBA analysis werc fractionated by gcl-filtration. 1t was then found that unsaturated monomcr and dimer are the major products from SM whiJe mono-, diand trimer consist mainly of the products from SG, suggosting the cxistcnce of two differcnt kinds of alginate lyases m the alga] extracts, The lyase act ivi t ics were h i g h t r in old tissucs of the frond and lower in young ones, and in addition higher in st-asons when alga] fronds cmbedcd zoosporangia than in othcr seasons, Carbazolc analysis for reaction products showed thai absorbancc incrcased rcmurkably at carlicr stages of incubation while absorbance in TBA analysis incrcased almost in parallel w i th i n c u b u t i o n time.

Isolation and Physico-chemical Properties of a Substance 334 from the Red Alga, Porphyra yezoensis Ueda

A novel UV-absorbing substance 334 was isolated in a crystalline form from a red algü, Porphyra yezoensis It was found to be a peptidal compound and to contain no aromaticy such äs bcnzenc, purine and pyrimidine origin, Elementary analysis indicated its chemical composition to be 42.98 % C, 6.22% H, 7 . 7 1 % N, 34.09% O and 9.0 % Na. Degradative studies indicated its peptidal portion to be glycinc and thrconine cxist ing in <jn equimolar ratio amounting to 27 % of the compound, Basing on IR, high resolution proton N M R , 1 C-NMR and mass sp^ctroscopy, its moleculai weight was calculated to be 298 with a chemical formula of C v , H ] 9 O 6 N 2 N a , Tfu· substance 334 has an excitation and fluorescence action spectra at 368 and 430 nm, respcctivcly. Further, it proccs^cs oxidation and reduction capacities, and the absorption maximum of the oxidized form was found at 334 nm and that of reducod form was at a wavelength shifted only very sljghtly toward longerside.

Purification and Characterization of Mannitol-l-Phosphatase in the Red Alga Caloglossa continua (Ceramiales, Rhodophyta).

Abstract: Purification of mannitol-l-phosphatase, an enzyme catalyzing the final step of mannitol biosynthesis, was first achieved in the mannitol-accumulating red alga Caloglossa continua (Okamura) King et Puttock. The enzyme was shown to be a monomer, since gel filtration and sodium dodecyl sulfate–polyacrylamide gel electrophoresis gave close values of apparent molecular weights of 28,500 and 30,200, respectively. The protein exhibited an isoelectric point of 4.8. The substrate specificity for mannitol-l-phosphate (MIP) was very high, and that for Km(MIP) was 0.41 mM. The catalytic activity was optimal at pH 7.4. The enzyme was activated by Mg2+, but was strongly inhibited by Ca2+, NaF, N-ethylmaleimide, and p-hydroxymercuribenzoic acid. Seawater levels of NaCl and physiological levels of mannitol also inhibited the activity by 50% or more. Changes in the concentrations of those ions and metabolites may regulate the biosynthesis of mannitol as an osmoregulant in vivo.

Isolation and examination of biochemical activity of epidermal whole cells from a red alga, galaxauara falcata.

Photoactive whole cells were isolated for the first time from a red alga, Galaxaura falcata KJELMAN, of the Chaetangiaceae. By means of proton uptake experiments, its optimum irradiation ntensity required for photosynthesis, effec of Ca2+, Mg2+, Mn2+ and Na+ both mono-and divalent ions, uncouplers and a non-ionic surfactant were examined. Photochemical 14CO2 fixation u der different monochromatic irradiation , and RuDP and PEP carboxylase activities n the cells were also studied and compared with those of thallus extracts. These results demonstrated the isolated cells to be biochemically active. An electron microscope study of the isolated whole cells was also performed.