Constitutive expression in gal7 mutants of Kluyveromyces lactis is due to internal production of galactose as an inducer of the Gal/Lac regulon.

The induction process of the galactose regulon has been intensively studied, but until now the nature of the inducer has remained unknown. We have analyzed a delta gal7 mutant of the yeast Kluyveromyces lactis, which lacks the galactotransferase activity and is able to express the genes of the Gal/Lac regulon also in the absence of galactose. We found that this expression is semiconstitutive and undergoes a strong induction during the stationary phase. The gal1-209 mutant, which has a reduced kinase activity but retains its positive regulatory function, also shows a constitutive expression of beta-galactosidase, suggesting that galactose is the inducer. A gal10 deletion in delta gal7 or gal1-209 mutants reduces the expression to under wild-type levels. The presence of the inducer could be demonstrated in both delta gal7 crude extracts and culture medium by means of a bioassay using the induction in gal1-209 cells. A mutation in the transporter gene LAC12 decreases the level of induction in gal7 cells, indicating that galactose is partly released into the medium and then retransported into the cells. Nuclear magnetic resonance analysis of crude extracts from delta gal7 cells revealed the presence of 50 microM galactose. We conclude that galactose is the inducer of the Gal/Lac regulon and is produced via UDP-galactose through a yet-unknown pathway.     

Human brain GABA transaminase tissue distribution and molecular expression.

Human brain gamma-aminobutyrate transaminase is differentially expressed in a tissue-specific manner. mRNA master dot-blot analysis for 50 different human tissues, including different brain regions and fetal tissues, provided a complete map of the tissue distribution. Genomic Southern analysis revealed that the gamma-aminobutyrate transaminase gene is a single copy, at least 15 kb in size. In addition, human brain gamma-aminobutyrate transaminase cDNA was expressed in Escherichia coli using a pGEX expression vector system. Catalytically active gamma-aminobutyrate transaminase was expressed in large quantities and the purified recombinant enzyme had kinetic parameters that were indistinguishable from those isolated from other mammalian brains. The human enzyme was inactivated by a well-known antiepileptic drug vigabatrin. Values of Ki and kinact were 1 mM and 0.35 min-1, respectively. Results from inactivation kinetics suggested that human gamma-aminobutyrate transaminase is more sensitive to the vigabatrin drug than the enzyme isolated from bovine brain.     

Bacterial endosymbiosis in amoebae

The large, free-living amoebae are inherently phagocytic. They capture, ingest and digest microbes within their phagolysosomes, including those that survive in other cells. One exception is an unidentified strain of Gram-negative, rod-shaped bacteria that spontaneously infected the D strain of Amoeba proteus and came to survive inside them. These bacteria established a stable symbiotic relationship with amoebae that has resulted in phenotypic modulation of the host and mutual dependence for survival.     

Continuous production of extracellular ultrafine calcite particles by the marine coccolithophorid alga Pleurochrysis carterae

A new procedure for the production of ultrafine calcite particles by the marine coccolithophorid alga Pleurochrysis carterae is reported. During continuous culture, calcite particles (coccoliths) were detached from the cell surface by optimized air-bubbling, which greatly reduced the damage associated with previous sonication methods. Detached calcite particles could be continuously recovered directly from the culture medium using a nylon mesh membrane filtration module. Cells remained viable and continued to produce coccoliths during culture. The optimum productivity of ultrafine calcite particles was 18 mg/l per day. These results demonstrate the potential for a continuous system for the photosynthetically driven removal of CO₂ and its fixation into ultrafine inorganic calcite particles. Correspondence to: T. Matsunaga     

GROWTH CHARACTERISTICS AND ANTIOXIDANT PROPERTIES OF THE BENTHIC DIATOM NAVICULA INCERTA (BACILLARIOPHYCEAE) FROM JEJU ISLAND,KOREA1

Benthic diatoms are a commonly used food source in shellfish aquaculture. Diatoms of the genus Navicula are the most abundant benthic diatoms occurring year‐round on the coast of Jeju Island, Korea. We isolated an axenic strain of N. incerta Grunow; estimated its growth characteristics under 27 different combinations of temperature, salinity, and nutrients; and determined its biochemical composition and antioxidant activities. The maximum specific growth rate (μ_max), defined as the increase in cell density per unit time, was 0.81–1.04 · d^?1, and the maximum cell density, 7.99 × 10⁵ cells · mL^?1, was reached at 0.88 · d^?1 μ_max, 20°C, 30 psu salinity, and F/2 nutrient concentration on day 12 of the culture period. The approximate cellular composition was as follows: 7.0 ± 0.04% protein, 1.7 ± 0.28% lipid, 12.8 ± 0.85% carbohydrate, 68.4 ± 0.09% ash, and 10.1 ± 0.44% moisture. The antioxidant properties of N. incerta were determined for various extracts. The rates of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) free‐radical scavenging for Neutrase and methanol extracts were 81.6% and 62.8%, respectively. Flavourzyme extract had a superoxide‐scavenging rate of 57.7%. Kojizyme and Ultraflo extracts had nitric‐oxide‐scavenging rates of 42.2% and 40.6%, respectively, significantly higher than commercial antioxidants, such as α‐tocopherol and butylated hydroxytoluene (BHT). The metal‐chelating activities of the methanol, Neutrase, and Termamyl extracts were 68.5%, 45.2%, and 41.2%, respectively, four to six times higher than commercial antioxidants. The Termamyl extract showed the highest linoleic acid peroxidation inhibition, exceeding α‐tocopherol and on par with BHT.     

Sex pheromone production and response in Korean populations of the diamondback moth, Plutella xylostella

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Yponomeutidae), is a worldwide pest of cruciferous crops. We examined the female pheromone production and male response to various pheromone blends in two Korean populations. Gas chromatography (GC) and GC‐mass spectrometry (MS) analyses of pheromone gland extracts revealed that females produce (Z)‐11‐hexadecenal (Z11‐16:Ald), (Z)‐11‐hexadecenyl acetate (Z11‐16:OAc), and (Z)‐11‐hexadecen‐1‐ol (Z11‐16:OH) in a ratio of 8:100:18. However, (Z)‐9‐tetradecenyl acetate (Z9‐14:OAc), a previously reported component of the sex attractant of a Canadian P. xylostella population was not detected in gland extracts of the Korean one. Field tests showed that Z11‐16:Ald and Z11‐16:OAc are essential for attraction of male moths, and the highest attraction is obtained with a 10:90 blend mimicking the blend found in gland extracts. Addition of 1 or 10% of Z11‐16:OH to the 10:90 blend of Z11‐16:Ald and Z11‐16:OAc significantly increased attraction. However, attraction was strongly antagonized by the addition of as little as 0.1% of Z9‐14:OAc to the most attractive ternary blend. The ternary blend of Z11‐16:Ald, Z11‐16:OAc, and Z11‐16:OH at a ratio of 10:90:1 was more effective at catching P. xylostella males than the Japanese three‐component blend or the Canadian four‐component blend in Korea. These results suggest that there is geographical variation in the pheromone systems of this species.     

Protective effect of a freshwater alga, <Emphasis Type="Italic">Spirogyra</Emphasis> sp., against lipid peroxidation in vivo zebrafish and purification of antioxidative compounds using preparative centrifugal partition chromatography

A freshwater alga, Spirogyra sp., collected in shallow ponds in South Korea, was evaluated for its antilipid peroxidative effect against 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced in vivo zebrafish, and antioxidative compounds from the alga were efficiently identified using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS⁺) online high-performance liquid chromatography (HPLC) and preparative centrifugal partition chromatography. The ethyl acetate fraction of Spirogyra sp. (SPE) in each fraction showed the strongest 2,2-diphenyl-1-picrylhydrazyl scavenging activity and significantly scavenged 2′,7′-dichlorodihydrofluorescein diacetate and diphenyl-1-pyrenylphosphine fluorescence, respectively, in AAPH-induced zebrafish embryo without any cytotoxicity in the concentrations between 25 and 50 μg mL^?1. The two main antioxidative compounds in SPE were confirmed by ABTS⁺ online HPLC and were identified as gallic acid and methyl gallate, respectively, by HPLC–diode array detection (DAD)–electrospray ionization (ESI)/mass spectrometry (MS), ¹H- and ¹³C-NMR. We conclude therefore that Spirogyra sp. is rich in gallic acid and methyl gallate, and it might be useful as a strong antilipid peroxidation material.