Characterization of cDNA of lycopene beta-cyclase responsible for a high level of beta-carotene accumulation in Dunaliella salina.

Lycopene beta-cyclase (Lyc-B) is the key enzyme in the catalysis of linear lycopene to form cyclic beta-carotene, an indispensable part of the photosynthetic apparatus and an important source of vitamin A in human and animal nutrition. Studies showing that the microalga Dunaliella salina can accumulate a high level of beta-carotene are lacking. We hypothesize that D. salina is closely involved with the catalytic mechanism of Lyc-B and the molecular regulation of its gene. In this study, we used RT-PCR and RACE-PCR to isolate a 2475 bp cDNA with a 1824 bp open reading frame, encoding a putative Lyc-B, from D. salina. Homology studies showed that the deduced amino acid sequence had a significant overall similarity with sequences of other green algae and higher plants, and that it shared the highest sequence identity, up to 64%, with Lyc-B of Chlamydomonas reinhardtii. Codon analysis showed that synonymous codon usage in the enzyme has a strong bias towards codons ending with adenosine. Two motifs were found in the Lyc-B sequence, one at the N terminus, for binding the hypothetical cofactor FAD, and the other was a substrate carrier motif in oxygenic organisms shared by an earlier carotenogenesis enzyme, phytoene desaturase, and Lyc-B. A tertiary structure prediction suggested that the catalytic or binding site structure within LycB from D. salina is superior to that of both H. pluvialis and C. reinhardtii. The LycB protein from D. salina was quite removed from that of H. pluvialis and C. reinhardtii in the phylogenetic tree. Taken as a whole, this information provides insight into the regulatatory mechanism of Lyc-B at the molecular level and the high level of beta-carotene accumulation in the microalga D. salina.     

盾叶薯蓣地上部分的三个新甾体皂甙

从盾叶薯蓣Dioscorea zingiberensis Wright地上部分分离鉴定了四个甾体皂甙,经鉴定甙A为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)]-β-D-葡萄吡喃糖甙;甙B为24α-羟基约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)]β-D-葡萄吡喃糖甙;甙C为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)][β-D-葡萄吡喃糖基(1→4)]-β-D-葡萄吡喃糖基;甙D为约莫皂甙元-3-O-[α-L-鼠李吡喃糖基(1→2)][β-D-葡萄吡喃糖基(1→3)]-β-D-葡萄吡喃糖甙。前三者为新化合物,分别命名为盾叶皂甙A_1、A_2、A_3(zingiberoside A_1、A_2、A_3),其中盾叶皂甙A_2的甙元为一新甾体皂甙元,命名为盾叶皂甙元(zingiberogenin)。     

Epidermal growth factor and insulin stimulate nuclear pore-mediated macromolecular transport in isolated rat liver nuclei

Fluorescence photobleaching was used to measure the effect of epidermal growth factor (EGF), insulin, and glucagon on the nuclear transport of fluorescent-labeled dextrans across the nuclear pore complex. EGF and insulin were found to stimulate transport approximately 200%, while boiling these polypeptide growth factors greatly diminished this enhancement activity. Glucagon demonstrated no enhancement effect. The nuclear transport enhancement effects were observed at EGF and insulin concentrations that elicit the various physiological responses, e.g., nanomolar range.     

我国某些常见化石硅藻的环境分析

本文详细研究了中国海表层沉积物中的常见化石硅藻,结果表明,这些种的分布范围及数量变化随环境的不同而变化。因此,根据柱状样品中这些种类数量的变化,能够推断古气候变化,恢复古地理环境,再现海平面波动历程,进而划分、对比第四系地层。     

Ionizing-radiation-induced damage in the DNA of cultured human cells. Identification of 8,5-cyclo-2-deoxyguanosine.

Epstein-Barr-virus-transformed peripheral-blood B-lymphocytes were gamma-irradiated at 0 degree C at doses from 10 to 100 Gy. The cells were immediately lysed and the DNA was isolated. Subsequently, the DNA was hydrolysed to 2'-deoxyribonucleosides with a mixture of DNAase I, venom and spleen exonucleases and alkaline phosphatase. The hydrolysate was dried, trimethylsilylated and analysed by capillary gas chromatography-mass spectrometry with selected-ion monitoring. The (5'R)- and (5'S)-diastereomers of 8,5'-cyclo-2'-deoxyguanosine were observed in a ratio of 1:3, and their formation was dose-dependent. It was possible to detect and characterize one such lesion in approx. 4 X 10(4) guanine nucleotide subunits of DNA.     

长滩果引种驯化研究

长滩果系罗汉果最佳品种。原产区分布于永福和临桂县交界400—600米山区,但不适应于低丘陵和平原地区,因而不能在低丘陵和平原地区推广。为了解决这个问题。采用了(1)选择湿润和半阴的生长环境;(2)采用适应性强的砧木;(3)促成栽培;(4)加强秋旱期的科学管理等措施并取得成功,试验结果表明长滩果产量和品质达到或略超过原产区水平。