Theoretical studies of the anti-tumor drug FR900482

Hartree-Fock and density functional theory (B3LYP) calculations were applied to the study of the anti-tumor drug FR900482 and some of its analogs. Optimum geometries were obtained and it was found that the most stable conformations feature the N-H bond of the aziridine ring nitrogen “down” and the oxygen bridge and aziridine nitrogen “up”. It was also found that the analog containing NH₂ (in place of the -CHO of the natural product) is the most prone to oxidation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. It seems that a simple name for FR900482 has not been adopted so far because there is still a search for the most stable analog.     

Theoretical studies of the reduction reaction of the anti-tumor drug FR900482

A number of analogs of the anti-tumor drug FR900482 have been investigated with quantum chemical calculations, at the HF/6-31G(d,p) and B3LYP levels from the point of view of their energy, optimum geometry and the energetics of the reduction reaction. It was found that the parent molecule is the most prone to reduction, followed closely by fluorine-containing analogs.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

An uncommon case of spontaneous conversion from AV re-entry tachycardia to AV nodal re-entry tachycardia in a patient with dual tachycardia

We report the case of a 46-year old patient in whom an electrophysiology study (EP) was performed due to paroxysmal supraventricular tachycardia documented in 12-lead ECG. During the EP study, supraventricular tachycardia was induced easily and it corresponded to orthodromic AV reentry tachycardia (AVRT) using a concealed left free wall accessory pathway. However, during the study AVRT spontaneously and repeatedly converted to the typical slow-fast AV node reentry tachycardia (AVNRT). Both accessory and AV nodal slow pathways were ablated, due to the finding that both AVRT and AVNRT were independently inducible during the EP study.     

Stabilization of human prostate acid phosphatase by cross-linking with diimidoesters

1. Modification of dimeric human prostate acid phosphatase (EC 3.1.3.2) by diimidoesters leads to the formation of water-soluble preparations of high enzymatic activity, resistant to denaturing agents. 2. Monomeric, dimeric, trimeric and tetrameric species were found in SDS-polyacrylamide gel electrophoresis of the phosphatase cross-linked with dimethyl-suberimidate, and dimeric, trimeric and tetrameric enzymatically active species on thin-layer Sephadex 200 gel filtration. This molecular pattern evidenced formation of the inter-subunit covalent linkages. All molecular forms are immunoreactive against the polyclonal rabbit anti-phosphatase antibodies. 3. The catalytic properties of the modified phosphatase are almost the same as those of the native enzyme. Differences in the optical properties between the modified and the native enzymes point to slight conformational transitions in the modified enzyme.     

Immunoreactivity of proteolytic degradation products of human prostatic acid phosphatase

Prostatic acid phosphatase (EC 3.1.3.2) was fragmented by trypsin and papain in the presence of sodium dodecyl sulphate. Trypsin-catalysed cleavage gave a peptide of 33 kDa which was subsequently trimmed to 18 kDa, 15 kDa and 13 kDa peptides. Even the small tryptic fragments reacted with antiphosphatase antibodies from rabbit serum and with monoclonal antibody mAb-14. Papain treatment under these conditions resulted in the release of a 40 kDa peptide which was gradually reduced to a 18 kDa peptide. The monoclonal antibody mAb-14 to the prostatic phosphatase was bound exclusively to the 50 kDa subunit of the phosphatase and to the 40 kDa peptide. The results suggest that the monoclonal antibody mAb-14 binding site represents a "local" sequence rather than a "conformational" one and does not require an extensive tertiary folding of the antigen molecule.     

Characterization of the END1 gene required for vacuole biogenesis and gluconeogenic growth of budding yeast.

The Saccharomyces cerevisiae END1 gene is required for formation or maintenance of the vacuole, for growth on non-fermentable carbon sources, for efficient mating and for growth at 37 degrees C. The END1 gene was cloned by complementation of the end1 mutation. Two end1 null mutants, constructed by disruption and deletion of the END1 gene, show features identical to the original end1 mutant. However, in this paper we correct a previous finding from our group that end1 is defective in internalization of the yeast pheromone alpha-factor. End1 mutants take up alpha-factor at the same rate as corresponding wild-type cells but the internalized pheromone is not degraded. Since whole cell respiration and respiratory control of end1 mitochondria are not impaired, it seems plausible that a defect in gluconeogenesis could partially account for the inability of end1 to grow on non-fermentable carbon sources. DNA sequence analysis of the END1 gene reveals a 3090-bp open reading frame capable of encoding a hydrophilic protein of 118 kd. The molecular mass of End1p was confirmed by immunoprecipitation. The predicted End1p sequence shows no significant similarity to other known protein sequences except for a short region of homology with the putative adenine nucleotide binding sites shared by a group of enzymes, notably ATPases.     

Influence of Potassium Deficiency on Photosynthesis,Chlorophyll Content,and Chloroplast Ultrastructure of Cotton Plants

In cotton (Gossypium hirsutum L.) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied. After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (P _N) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply. Decreased leaf P _N of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves. Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading. K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues.     

DNA damage checkpoint kinase Chk2 triggers replicative senescence

Telomere shortening in normal human cells causes replicative senescence, a p53-dependent growth arrest state, which is thought to represent an innate defence against tumour progression. However, although it has been postulated that critical telomere loss generates a 'DNA damage' signal, the signalling pathway(s) that alerts cells to short dysfunctional telomeres remains only partially defined. We show that senescence in human fibroblasts is associated with focal accumulation of gamma-H2AX and phosphorylation of Chk2, known mediators of the ataxia-telangiectasia mutated regulated signalling pathway activated by DNA double-strand breaks. Both these responses increased in cells grown beyond senescence through inactivation of p53 and pRb, indicating that they are driven by continued cell division and not a consequence of senescence. gamma-H2AX (though not Chk2) was shown to associate directly with telomeric DNA. Furthermore, inactivation of Chk2 in human fibroblasts led to a fall in p21(waf1) expression and an extension of proliferative lifespan, consistent with failure to activate p53. Thus, Chk2 forms an essential component of a common pathway signalling cell cycle arrest in response to both telomere erosion and DNA damage.     

Senescence and hyperspectral reflectance of cotton leaves exposed to ultraviolet-B radiation and carbon dioxide

The objectives of this study were to determine the effects of UV-B radiation and atmospheric carbon dioxide concentrations ([CO(2)]) on leaf senescence of cotton by measuring leaf photosynthesis and chlorophyll content and to identify changes in leaf hyperspectral reflectance occurring due to senescence and UV-B radiation. Plants were grown in controlled-environment growth chambers at two [CO(2)] (360 and 720 micro mol mol(-1)) and three levels of UV-B radiation (0, 7.7 and 15.1 kJ m(-2) day(-1)). Photosynthesis, chlorophyll, carotenoids and phenolic compounds along with leaf hyperspectral reflectance were measured on three leaves aged 12, 21 and 30 days in each of the treatments. No interaction was detected between [CO(2)] and UV-B for any of the measured parameters. Significant interactions were observed between UV-B and leaf age for photosynthesis and stomatal conductance. Elevated [CO(2)] enhanced leaf photosynthesis by 32%. On exposure to 0, 7.7 and 15.1 kJ of UV-B, the photosynthetic rates of 30-day-old leaves compared with 12-day-old leaves were reduced by 52, 76 and 86%, respectively. Chlorophyll pigments were not affected by leaf age at UV-B radiation of 0 and 7.7 kJ, but UV-B of 15.1 kJ reduced the chlorophylls by 20, 60 and 80% in 12, 21 and 30-day-old leaves, respectively. The hyperspectral reflectance between 726 and 1142 nm showed interaction for UV-B radiation and leaf age. In cotton, leaf photosynthesis can be used as an indicator of leaf senescence, as it is more sensitive than photosynthetic pigments on exposure to UV-B radiation. This study revealed that, cotton leaves senesced early on exposure to UV-B radiation as indicated by leaf photosynthesis, and leaf hyperspectral reflectance can be used to detect changes caused by UV-B and leaf ageing.     

p21-Mediated nuclear retention of cyclin B1-Cdk1 in response to genotoxic stress

G2 arrest of cells suffering DNA damage in S phase is crucial to avoid their entry into mitosis, with the concomitant risks of oncogenic transformation. According to the current model, signals elicited by DNA damage prevent mitosis by inhibiting both activation and nuclear import of cyclin B1-Cdk1, a master mitotic regulator. We now show that normal human fibroblasts use additional mechanisms to block activation of cyclin B1-Cdk1. In these cells, exposure to nonrepairable DNA damage leads to nuclear accumulation of inactive cyclin B1-Cdk1 complexes. This nuclear retention, which strictly depends on association with endogenous p21, prevents activation of cyclin B1-Cdk1 by Cdc25 and Cdk-activating kinase as well as its recruitment to the centrosome. In p21-deficient normal human fibroblasts and immortal cell lines, cyclin B1 fails to accumulate in the nucleus and could be readily detected at the centrosome in response to DNA damage. Therefore, in normal cells, p21 exerts a dual role in mediating DNA damage-induced cell cycle arrest and exit before mitosis. In addition to blocking pRb phosphorylation, p21 directly prevents mitosis by inactivating and maintaining the inactive state of mitotic cyclin-Cdk complexes. This, with subsequent degradation of mitotic cyclins, further contributes to the establishment of a permanent G2 arrest.