Anti-HBV and cytotoxic activities of pyranocoumarin derivatives

Four natural pyranocoumarins clausenidin (1), nordentatin (2), clausarin (3), and xanthoxyletin (4) were isolated from the medicinal plant Clausena excavata. Recently, we found that 1 and 2 suppressed hepatitis B virus surface antigen in HepA2 cells, and in addition, 1–3 showed cytotoxic activity against four human cancer cell lines (A549, MCF7, KB, and KB-VIN). To explore the SAR of 1–4, 17 pyranocoumarin analogues (5–21) were designed and synthesized. Among these analogues, 5 and 10 were the most potent against hepatitis B virus with EC₅₀ values of 1.14 and 1.34 μM, respectively. The most interesting result in the cytotoxicity assay was the significant activity of 1, 5, and 6 against the multi-drug resistant cell line, KB-VIN, without activity against the KB cell line. These data suggest that these three compounds could be useful hits for developing MDR-inverse drugs.     

Removal of cadmium ions in wastewater through biosorption

Cadmium ions in wastewater can be removed by biosorption on to Acinetobacter calca var. antratus, isolated from a wastewater sample from a copper refinery. There are two equillibrium states: the first, which is reached quickly, is probably direct adsorption, and the second may be due to the release of ion adsorption materials by lysed cells.The authors are with the Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan 10764, ROC.     

Evidence Against Phenotypic Mixing Between Bacteriophage T4 Wild Type and T4v?

In a recent publication Shames et al. (1973) concluded that the UV-specific T4 endonuclease (a repair enzyme coded for by the gene v of wild-type T4) is a component of extracellular phage, which is injected into the host cell and can perform an early repair step without requiring gene expression. This notion is, however, not supported by results presented in this paper. Lysates obtained from mixed multiple infection of Escherichia coli cells with T4v(1) (-) and T4v(+) (or T4v(2) (-) and T4v(+)) failed to show the expected phenotypic mixing, i.e., incorporation of UV endonuclease into capsids of v(-) phages resulting in recognizable repair. The fraction of v(+) and v(-) particles in such lysates was determined by single-plaque analysis before and after irradiation with a UV dose at which virtually all survivors are particles having undergone repair. Even though our mixed infection conditions were most favorable for the possible occurrence of phenotypic mixing, none out of several hundred individual plaques from survivors were found to be genotypically v(-), whereas 30 were expected in the case that phenotypically mixed v(-) particles were repaired like T4v(+). Our failure to observe phenotypic mixing suggests that the data by Shames et al. reflect intracellular synthesis of endonuclease after phage infection.     

The phycobilisome, a light-harvesting complex responsive to environmental conditions.

Photosynthetic organisms can acclimate to their environment by changing many cellular processes, including the biosynthesis of the photosynthetic apparatus. In this article we discuss the phycobilisome, the light-harvesting apparatus of cyanobacteria and red algae. Unlike most light-harvesting antenna complexes, the phycobilisome is not an integral membrane complex but is attached to the surface of the photosynthetic membranes. It is composed of both the pigmented phycobiliproteins and the nonpigmented linker polypeptides; the former are important for absorbing light energy, while the latter are important for stability and assembly of the complex. The composition of the phycobilisome is very sensitive to a number of different environmental factors. Some of the filamentous cyanobacteria can alter the composition of the phycobilisome in response to the prevalent wavelengths of light in the environment. This process, called complementary chromatic adaptation, allows these organisms to efficiently utilize available light energy to drive photosynthetic electron transport and CO2 fixation. Under conditions of macronutrient limitation, many cyanobacteria degrade their phycobilisomes in a rapid and orderly fashion. Since the phycobilisome is an abundant component of the cell, its degradation may provide a substantial amount of nitrogen to nitrogen-limited cells. Furthermore, degradation of the phycobilisome during nutrient-limited growth may prevent photodamage that would occur if the cells were to absorb light under conditions of metabolic arrest. The interplay of various environmental parameters in determining the number of phycobilisomes and their structural characteristics and the ways in which these parameters control phycobilisome biosynthesis are fertile areas for investigation.     

Cytochrome c1 complexes.

Cytochrome c1 forms an active complex with cytochrome c as previously reported (Chiang, Y. L., Kaminsky, L. S., and King, T. E. (1976) J. Biol. Chem. 251, 29-36). It also forms a complex with cytochrome oxidase with heme ratio of 1:1. This cytochrome c1.oxidase complex has been purified by ammonium sulfate fractionation and is stable in media of high ionic strength (greater than 0.1 M) but dissociates as the pH deviates from neutral. The purified cytochrome c1 aggregates to an oligomer, presumably a pentamer. No agent has been found to depolymerize isolated c1 without denaturation. However, in the cytochrome c1.oxidase complex, these two cytochromes apparently were depolymerized to form smaller aggregates, if not monomeric units, as judged by sedimentation behavior. Cytochrome c1 also forms a ternary complex with cytochrome c and oxidase in the heme ratio of 1:1:1. This complex can be prepared by any of the following four methods: (i) c1 + c + oxidase: (ii) c1.c complex + oxidase; (iii) c1 + c.oxidase complex: or (iv) c + c1.oxidase complex. The mode of formation of these complexes is all from pure protein-protein interactions. Cytochrome c1 is also incorporated into phospholipid vesicles and these vesicles show about 200 molecules of phospholipid/cytochrome c1 in terms of heme. The spectrophotometric, circular dichroic, sedimentation behavior and enzymic properties of these complexes have been investigated.     

Absolute configuration of a chiral CHD group via neutron diffraction: confirmation of the absolute stereochemistry of the enzymatic formation of malic acid

Neutron diffraction has been used to monitor the absolute stereochemistry of an enzymatic reaction. (-)(2S)malic-3-d acid was prepared by the action of fumarase on fumaric acid in D2O. After a large number of cations were screened, it was found that (+)(R) alpha-phenylethylamine forms the large crystals necessary for a neutron diffraction analysis. The subsequent structure determination showed that (+)(R) alpha-phenylethylammonium (-)(2S)malate-3-d has an absolute configuration of R at the CHD site (i.e., the C3 carbon of malate). This result confirms the absolute stereochemistry of fumarate-to-malate transformation as catalyzed by the enzyme fumarase.     

Expression of a gene encoding β‐ureidopropionase is critical for pollen germination in tomatoes

Global warming has seriously decreased world crop yield. High temperatures affect development, growth and, particularly, reproductive tissues in plants. A gene encoding β‐ureidopropionase (SlUPB1, EC 3.5.1.6) was isolated from the stamens of a heat‐tolerant tomato (CL5915) using suppression subtractive hybridization. SlUPB1 catalyzes the production of β‐alanine, the only β‐form amino acid in nature. In the anthesis stage, SlUPB1 expression in CL5915 stamens, growing at 35/30°C (day/night), was 2.16 and 2.93 times greater than that in a heat‐sensitive tomato (L4783) cultivated at 30/25°C or 25/20°C, respectively. Transgenic tomatoes, upregulating SlUPB1 in L4783 and downregulating SlUPB1 in CL5915, were constructed, and the amount of β‐alanine measured by liquid chromatography‐electrospray ionization‐mass spectrometry in the transgenic overexpression of SlUPB1 was higher than that of L4783. However, the β‐alanine in the transgenics downregulating SlUPB1 was significantly lower than the β‐alanine of CL5915. Pollen germination rates of these transgenics were analyzed under different developmental and germinating temperatures. The results indicated that germination rates of transgenics overexpressing SlUPB1 were higher than germination rates of the background tomato L4783. Germination rates of transgenics downregulating SlUPB1 were significantly lower than germination rates of background tomato CL5915, indicating the necessity of functional SlUPB1 for pollen germination. Pollen germinating in the buffer with the addition of β‐alanine further indicated that β‐alanine effectively enhanced pollen germination in tomatoes with low SlUPB1 expression. Together, these results showed that the expression of SlUPB1 is important for pollen germination, and β‐alanine may play a role in pollen germination under both optimal and high temperatures.