Three saponins from Oxytropis species.

Three flavonoids and three saponins have been isolated from Oxytropis species. Their structures were determined as isorhamnetin-3-O-beta-D-glucoside, rhamnetin-3-O-beta-D-galactoside, apigenin, 3-O-[alpha-L-rhamnopyranosyl (1----2)-beta-D-glucopyranosyl(1----4)-beta-D-glucuronopyranosyl]+ ++soyasapogenol B, 3-O-[beta-D-glucopyranosyl(1----2)-beta-D-glucuronopyranosyl] azukisapogenol and a new saponin 3-O-[beta-D-glucopyranosyl(1----2)-beta-D-glucopyranosyl]-25-O-alpha-L- rhamnopyranosyl-(20S,24S)-3 beta,16 beta, 20,24,25-pentahydroxy-9,19-cycloanostane.     

Mutational analysis of slyD, an Escherichia coli gene encoding a protein of the FKBP immunophilin family

slyD encodes a 196 amino acid polypeptide that is a member of the FKBP family of cis–trans peptidyl–prolyl isomerases (PPIases). slyD mutations affect plaque formation by the phage φX174 by blocking the action of the phage lysis protein E. Here we describe the selection of a set of spontaneous slyD mutations conferring resistance to the expression of gene E from a plasmid. These mutations occur disproportionately in residues of SlyD that, based on the structure of the prototype mammalian FKBP12, make ligand contacts with immunosuppressing drug molecules or are conserved in other FKBP proteins. A wide variation in the plating efficiency of φX174 on these E  ^R strains is observed, relative to the parental, indicating that these alleles differ widely in residual SlyD activity. Moreover, it is found that slyD mutations cause significant growth rate defects in Escherichia coli B and C backgrounds. Finally, overexpression of slyD causes filamentation of the host. Thus, among the FKBP genes found in organisms across the evolutionary spectrum, slyD is unique in having three distinct drug-independent phenotypes.     

Ligand binding to cytochrome c peroxidase from Pseudomonas aeruginosa

The high potential heme site of Pseudomonas cytochrome c peroxidase has His and Met as ligands. On reduction, the Fe-met bond becomes photosensitive. Following photolysis, the bond reforms with a half-time of 35 ps. The low potential heme peroxidatic site of the fully reduced enzyme has been shown to bind to a range of ligands. The compounds with carbon monoxide, methyl, ethyl, n-butyl, and t-butyl isonitriles have been investigated by laser flash photolysis. All are photosensitive and show different degrees of geminate recombination of ligand in the picosecond and nanosecond time ranges. Carbon monoxide shows the least effect. The three straight-chain isonitriles show about 50% geminate recombination with half-times of the order of 10 ns. t-Butyl isonitrile shows more and faster recombination. These results imply considerable freedom of movement within the active site for the smaller ligands.     

Post-translational modifications of protein in response to ionizing radiation

Based on central dogma of genetics, protein is the embodiment and executor of genetic function, post-translational modifications (PTMs) of protein are particularly important and involved in almost all aspects of cell biology and pathogenesis. Studies have shown that ionizing radiation (IR) alters gene expression much more profoundly and a broad variety of cell-process pathways, lots of proteins are modified and activated. Our understanding of the protein in response to ionizing radiation is steadily increasing. Among the various biological processes known to induce radioresistance, PTMs have attracted marked attention in recent years. The present review summarizes the latest knowledge about how PTMs response to ionizing radiation and pathway analysis were conducted. The data provided insights into biological effects of IR and contributing to the development of novel IR-based strategies.     

Acquisition of an additional internal cleavage site differentially affects the ability of pseudorabies virus to multiply in different host cells.

The translocation of the 325 leftmost bp of the genome of pseudorabies virus (PrV) to the internal junction between the L and S components confers upon the virus a growth advantage relative to wild-type PrV in chicken embryo fibroblasts (CEFs) and chickens and a growth disadvantage in rabbit kidney (RK) cells and mice. To clarify the molecular basis for the species-specific growth characteristics of the translocation mutants, we have compared several parameters of the virus growth cycle in CEFs and RK cells infected with wild-type PrV and with translocation mutants. The salient findings are as follows. (i) The synthesis of early-late and late proteins is not as effective in CEFs as it is in RK cells, and these proteins, in particular, the major capsid proteins, accumulate less abundantly in CEFs than in RK cells. (ii) Cleavage of concatemeric DNA to genome-size molecules is also not as effective in CEFs as it is in RK cells. (iii) The internal junction present in translocation mutants is a functional cleavage site. (iv) In RK cells, translocation mutants are hypercleaved and a significant proportion of the total viral DNA is cleaved into subgenomic fragments. (v) In CEFs infected with translocation mutants, subgenomic fragments also accumulate but most of the viral DNA remains in concatemeric form. A model which postulates that the cell-specific growth advantage or disadvantage of the translocation mutants is related to the presence of a second cleavage site within their genomes and is affected by the efficiency of cleavage of concatemeric DNA in particular infected cell types is presented. The significance of these findings as they relate to the evolution of herpesviruses with class 2- and class 3-like genomes is discussed.     

Inhibition of lipase-catalyzed hydrolysis of sunflower oil in AOT/isooctane reversed micelles

The hydrolysis of sunflower oil using Candida cylindracea lipase in reversed micelles of AOT/isooctane was investigated. The inhibition caused by substrate and hydrolysis products has been found in the process of reaction. It was revealed that the extent of inhibition caused by oleic acid was higher than that caused by glycerol, and was much more serious in the case of the mixture of hydrolysis products. Moreover, with the initial addition of glycerol into the reaction mixture, the stability of lipase could be increased during the hydrolysis of sunflower oil in reversed micelles. We thank the National Natural Science Foundation of China for the financial support of this work. We also thank Prof. Xu, Jia-li for his contributions to this work.