Steroidal constituents of Solanum xanthocarpum

From the extract of the fruits of Solanum xanthocarpum, cycloartanol (I), cycloartenol (II), sitosterol (III), stigmasterol (IV), campesterol (V), cholesterol (VI), sitosteryl glucoside (VII), stigmasteryl glucoside (VIII), solamargine (IX), and β-solamargine (X) were identified and an isolated steroid (XI) was identical with 4α-methyl-(24R)-ethylcholest-7-en-3β-ol synthesized from carpesterol.     

Evidence for Conservative (Two-Progeny) DNA Double-Strand Break Repair

The double-strand break repair models for homologous recombination propose that a double-strand break in a duplex DNA segment is repaired by gene conversion copying a homologous DNA segment. This is a type of conservative recombination, or two-progeny recombination, which generates two duplex DNA segments from two duplex DNA segments. Transformation with a plasmid carrying a double-strand gap and an intact homologous DNA segment resulted in products expected from such conservative (two-progeny) repair in Escherichia coli cells with active E. coli RecE pathway (recBC sbcA) or with active bacteriophage λ Red pathway. Apparently conservative double-strand break repair, however, might result from successive events of nonconservative recombination, or one-progeny recombination, which generates only one recombinant duplex DNA segment from two segments, involving multiple plasmid molecules. Contribution of such intermolecular recombination was evaluated by transformation with a mixture of two isogenic parental plasmids marked with a restriction site polymorphism. Most of the gap repair products were from intramolecular and, therefore, conservative (two-progeny) reaction under the conditions chosen. Most were conservative even in the absence of RecA protein. The double-strand gap repair reaction was not affected by inversion of the unidirectional replication origin on the plasmid. These results demonstrate the presence of the conservative (two-progeny) double-strand break repair mechanism. These experiments do not rule out the occurrence of nonconservative (one-progeny) recombination since we set up experimental conditions that should favor detection of conservative (two-progeny) recombination.     

Nematolysosomes (Elongate Lysosomes) in Rat Hepatocytes: Their Distribution, Microtubule Dependence, and Role in Endocytic Transport Pathway

The distribution of lysosomes in rat hepatocytes was examined by three-dimensional electron microscopy combined with acid phosphatase (ACPase) cytochemistry. In the 2-μm-thick sections observed under 200- or 1000-kV TEM, it was apparent that ACPase activity localized on elongate lysosomes (we refer to them as nematolysosomes) with a diameter of 70-100 nm and lengths of several micrometers, as well as spherical lysosomes and trans-Golgi cisternae. Though most spherical lysosomes were located within the pericanalicular region, nematolysosomes were widely distributed throughout the hepatocytes. Typically, it appeared that the nematolysosomes elongated from the subsinusoidal region to the pericanalicular-Golgi complex area and they frequently formed a network at the cell periphery along the sinusoidal front. Furthermore, the formation of nematolysosomes was independent of new protein synthesis, but highly dependent on the integrity of microtubules. After a 6-8 h colchicine treatment, nematolysosomes were shrunk and/or fragmented, becoming roughly spherical lysosomes scattered throughout the cells. Nematolysosomes recovered their normal profiles after 24 h due to the reversible effect of the drug on microtubules. When the hepatocytes were exposed to horseradish peroxidase (HRP) in vitro or in vivo, HRP was quickly sequestered in nematolysosome-like structures via pinocytosis from the sinusoidal surface and transported to an area near the Golgi complex. These findings raise the possibility that the nematolysosomes engage in microtubule-dependent transport of macromolecules from the sinusoidal circulation to the Golgi complex area.     

Specific binding of Thiobacillus ferrooxidans RbcR to the intergenic sequence between the rbc operon and the rbcR gene.

The presence of two sets (rbcL1-rbcS1 and rbcL2-rbcS2) of rbc operons has been demonstrated in Thiobacillus ferrooxidans Fe1 (T. Kusano, T. Takeshima, C. Inoue, and K. Sugawara, J. Bacteriol. 173:7313-7323, 1991). A possible regulatory gene, rbcR, 930 bp long and possibly translated into a 309-amino-acid protein, was found upstream from the rbcL1 gene as a single copy. The gene is located divergently to rbcL1 with a 144-bp intergenic sequence. As in the cases of the Chromatium vinosum RbcR and Alcaligenes eutrophus CfxR, T. ferrooxidans RbcR is thought to be a new member of the LysR family, and these proteins share 46.5 and 42.8% identity, respectively. Gel mobility shift assays showed that T. ferrooxidans RbcR, produced in Escherichia coli, binds specifically to the intergenic sequence between rbcL1 and rbcR. Footprinting and site-directed mutagenesis experiments further demonstrated that RbcR binds to overlapping promoter elements of the rbcR and rbcL1 genes. The above data strongly support the participation of RbcR in regulation of the rbcL1-rbcS1 operon and the rbcR gene in T. ferrooxidans.     

The GS-X Pump in Plant, Yeast, and Animal Cells: Structure, Function, and Gene Expression

This review addresses the recent molecular identification of several members of the glutathione S-conjugate (GS-X) pump family, a new class of ATP-binding cassette (ABC) transporters responsible for the elimination and/or sequestration of pharmacologically and agronomically important compounds in mammalian, yeast and plant cells. The molecular structure and function of GS-X pumps encoded by MRP, cMOAT, YCF1. and AtMRP genes, have been conserved throughout molecular evolution. The physiologic function of GS-X pumps is closely related with cellular detoxification, oxidative stress, inflammation, and cancer drug resistance. Coordinated expression of GS-X pump genes, e.g., MRP1 and YCF1, and -glutamylcystaine synthetase, a rate-limiting enzyme of cellular glutathione (GSH) biosynthesis, has been frequently observed.     

Cellular Localization and Expression of Template-Activating Factor I in Different Cell Types

Template-activating factors I (TAF-I) α and β have been identified as chromatin remodeling factors from human HeLa cells. TAF-Iβ corresponds to the protein encoded by thesetgene, which was found in an acute undifferentiated leukemia as a fusion version with thecangene via chromosomal translocation. To determine the localization of TAF-I, we raised both polyclonal and monoclonal antibodies against TAF-I. The proteins that react to the antibodies are present not only in human cells but also in mouse, frog, insect, and yeast cells. The mouse TAF-I homologue is ubiquitous in a variety of tissue cells, including liver, kidney, spleen, lung, heart, and brain. It is of interest that the amounts of TAF-Iα and β vary among hemopoietic cells and some specific cell types do not contain TAF-Iα. The level of the TAF-I proteins does not change significantly during the cell cycle progression in either HeLa cells synchronized with an excess concentration of thymidine or NIH 3T3 cells released from the serum-depleted state. TAF-I is predominantly located in nuclei, while TAF-I that is devoid of its acidic region, the region which is essential for the TAF-I activity, shows both nuclear and cytoplasmic localization. The localization of TAF-I in conjunction with the regulation of its activity is discussed.     

Enzymological Characteristics of the Hyperthermostable NAD-Dependent Glutamate Dehydrogenase from the Archaeon Pyrobaculum islandicum and Effects of Denaturants and Organic Solvents

NAD-dependent glutamate dehydrogenase (l-glutamate:NAD oxidoreductase, deaminating; EC 1.4.1.2) was purified to homogeneity from a crude extract of the continental hyperthermophilic archaeon Pyrobaculum islandicum by two successive Red Sepharose CL-4B affinity chromatographies. The enzyme is the most thermostable NAD-dependent dehydrogenase found to date; the activity was not lost after incubation at 100°C for 2 h. The enzyme activity increased linearly with temperature, and the maximum was observed at ca. 90°C. The enzyme has a molecular mass of about 220 kDa and consists of six subunits with identical molecular masses of 36 kDa. The enzyme required NAD as a coenzyme for l-glutamate deamination and was different from the NADP-dependent glutamate dehydrogenase from other hyperthermophiles. The K_m values for NAD, l-glutamate, NADH, 2-oxoglutarate, and ammonia were 0.025, 0.17, 0.0050, 0.066, and 9.7 mM, respectively. The enzyme activity was significantly increased by the addition of denaturants such as guanidine hydrochloride and some water-miscible organic solvents such as acetonitrile and tetrahydrofuran. When fluorescence of the enzyme was measured in the presence of guanidine hydrochloride, a significant emission spectrum change and a shift in the maximum were observed but not in the presence of urea. These results indicate that this hyperthermophilic enzyme may have great potential in applications to biosensor and bioreactor processes.During the past decade, many anaerobic hyperthermophiles growing at a temperature near or above the boiling point of water have been isolated from marine and continental volcanic environments (1). The interest in hyperthermophiles has been rapidly expanding. In particular, interest is focused on understanding the adaptation mechanisms that allow the metabolism to function and the biomolecules, such as protein, enzyme, and DNA, to remain intact at extremely high temperature. Most hyperthermophiles belong to Archaea, the third domain of life (22), and evolutionary attention has been paid to their biomolecules because they may be the most slowly evolving or primitive group of microorganisms yet discovered. In addition, enzymes from the hyperthermophiles have a large biotechnological potential (2, 6). Of the enzymes from hyperthermophiles, glutamate dehydrogenase (GluDH) (EC 1.4.1.4., glutamate:NADP oxidoreductase) is one of the enzymes for which the most abundant information concerning enzymological properties and the relationships between structure and function has been obtained. Extremely thermostable NADP-dependent GluDHs have been purified from Pyrococcus furiosus (5, 18, 20), Pyrococcus woesei (18), Thermococcus litoralis (14, 19), and Thermococcus profundus (11). The gdhA gene of Pyrococcus furiosus (8, 9) has been cloned and sequenced, and the structural difference between the GluDHs of Pyrococcus furiosus, T. litoralis, and Clostridium symbiosum has been investigated to elucidate protein thermostability (3). In addition, a key role of the ion pair networks in maintaining the structure stability of Pyrococcus furiosus GluDH at an extremely high temperature has been indicated (24). However, information about hyperthermostable GluDH is limited so far to that regarding marine hyperthermophilic species of the order Thermococcales such as Pyrococcus and Thermococcus.In the course of investigating GluDH distribution in hyperthermophilic archaea, we found the activity of NAD-dependent GluDH (EC 1.4.1.2) in the cell extract of a continental hyperthermophilic archaeon, Pyrobaculum islandicum. This is the first example of the occurrence of NAD-dependent GluDH in anaerobic hyperthermophilic archaea. In general, the physiological function of NAD-dependent GluDH is known to be different from that of NADP-dependent GluDH (17). In addition, the NAD-dependent GluDH may be expected to be more preferable for application than the NADP-dependent enzyme, because NAD and NADH are much cheaper than NADP and NADPH, respectively (4, 23). Thus, we purified the enzyme from P. islandicum for characterization. We describe here the characteristics of this GluDH with emphasis on its high stability in some denaturants and organic solvents.