Substitution of hydrazones for the 4' carbonyl on abscisic acid rendered it ineffective in a rapid stomatal–opening–inhibition bioassay

A rapid stomatal bioassay to test abscisic acid (ABA)–like inhibition of stomatal opening was elaborated. The assay was sensitive to low concentrations of ABA (>50% inhibition of opening at 0.02 μ M (+)-S-ABA) and was insensitive to 20 μ M (+)-S-ABA-1 -(methyl ester), which is consistent with previous work, With the original intent of developing anti-idiotypic antibodies, we made conjugates of ABA at the 4'carbonyl because of its accessibility and known requirements for other positions of the ABA molecule in siomatal signal transduction. We found that these conjugates lacked ABA-like activity and did not interfere with (+)-S-ABA in the stomatal bioassay, implying the importance of the 4'carbonyl. These observations cast doubt on the feasibility of using anti-idiolypic antibodies produced through the use of 4'-substituted ABA for the isolation of a guard-cell ABA receptor.     

Thyrotropin alters the utilization of thyroglobulin's hormonogenic sites

We injected rabbits and guinea pigs with bovine thyrotropin (TSH) daily for 3 days, while controls received saline. All animals received sodium [125I]iodide on the second day, and thyroglobulin was purified from the thyroids of each group by gel filtration. Hormonogenic tryptic peptides from each S-cyanoethylated thyroglobulin preparation were isolated by high performance liquid chromatography, and their amino acid sequences were determined, permitting their localization within the thyroglobulin polypeptide chain by comparison with cDNA-derived sequences from bovine and human thyroglobulins. Thyroglobulins from the saline-injected rabbits and guinea pigs contained the same four major hormonogenic sites, designated A-D, previously described (Dunn, J. T., Anderson, P. C., Fox, J. W., Fassler, C. A., Dunn, A. D., Hite, L. A., and Moore, R. C. (1987) J. Biol. Chem. 262, 16948-16952). In both species, sites A and C were the major loci for thyroxine and triiodothyronine, respectively. However, site D in the guinea pig had a greater ratio of [125I]thyroxine to [127I]thyroxine than did site A, whereas the reverse was true in the rabbit. TSH administration produced the following changes in thyroglobulins of both species, relative to controls: 1) an increase in the ratio of [125I]triiodothyronine to [125I] thyroxine (rabbit, 0.29 versus 0.17; guinea pig, 0.19 versus 0.08), with the increase in triiodothyronine principally at site C; 2) a marked increase in 125I/127I and in thyroxine formation at site D (14.1% of thyroglobulin's thyroxine versus 9.8% in rabbits, 24 versus 13% in guinea pigs); 3) a corresponding decrease in thyroxine formation at site A (33 versus 43% in rabbits, 30 versus 46% in guinea pigs); and 4) a sharp increase in conversion of thyroglobulin's N-terminal 125I-labeled approximately 20 kDa hormone-rich iodopeptide, which contains site A, to a 125I-labeled approximately 15-kDa (rabbit) or 125I-labeled approximately 13-kDa (guinea pig) form, reflecting probable peptide bond cleavage. Our results show that TSH alters both the structure of the thyroglobulin molecule and the priority of utilization of its hormonogenic sites. We conclude that these changes are important to TSH's enhancement of thyroid hormone synthesis.     

Genetic analysis of lipopolysaccharide core biosynthesis by Escherichia coli K-12: insertion mutagenesis of the rfa locus.

Tn10 insertions were selected on the basis of resistance to the lipopolysaccharide (LPS)-specific bacteriophage U3. The majority of these were located in a 2-kilobase region within the rfa locus, a gene cluster of about 18 kb that contains genes for LPS core biosynthesis. The rfa::Tn10 insertions all exhibited a deep rough phenotype that included hypersensitivity to hydrophobic antibiotics, a reduction in major outer membrane proteins, and production of truncated LPS. These mutations were complemented by a Clarke-Carbon plasmid known to complement rfa mutations of Salmonella typhimurium, and analysis of the insert from this plasmid showed that it contained genes for at least six polypeptides which appear to be arranged in the form of a complex operon. Defects in two of these genes were specifically implicated as the cause of the deep rough phenotype. One of these appeared to be rfaG, which encodes a function required for attachment of the first glucose residue to the heptose region of the core. The other gene did not appear to be directly involved in determination of the sugar composition of the core. We speculate that the product of this gene is involved in the attachment of phosphate or phosphorylethanolamine to the core and that it is the lack of one of these substituents which results in the deep rough phenotype.     

Dietary carbohydrate dictates development of Type 2 diabetes in the Nile rat

Amount and type of dietary carbohydrate (CHO), as well as the CHO:fat ratio, are thought to be critical for both the rate of development and severity of Type 2 diabetes mellitus. Thus, these nutritional considerations were examined in the previously described “spontaneous” model of diabetes and metabolic syndrome, the Nile rat. Weanling male Nile rats (n=92) were fed semipurified diets, modifying glycemic index and load by changing the amount of fiber or altering the CHO:fat ratio. Random and fasting blood glucose and body weight were assessed, and diabetes was characterized in terms of blood glucose, relevant plasma and liver parameters, food and water intake and terminal organ weights. Nile rats fed with hiCHO became more hyperglycemic than rats fed with modCHO (P<.05), while loCHO and hiCHO+hiFiber rats remained essentially normoglycemic. Liver lipid and glycogen accumulation was associated with severe hyperlipemia in diabetic rats, analogous to metabolic syndrome in humans. Advanced diabetes was linked to liver and kidney damage and elevated blood urea nitrogen with weight loss. Dispersing dietary CHO by fiber or replacing it by moderate fat (reducing the glycemic index and load) delayed the onset of diabetes but did not prevent signs of insulin resistance. A very low content of dietary CHO (high fat) seemed to prevent even these early indicators of insulin resistance. Thus, the Nile rat represents a novel CHO-sensitive model for study of Type 2 diabetes that reliably follows the course of disease in humans.     

A high-throughput screen for identification of molecular mimics of Smac/DIABLO utilizing a fluorescence polarization assay

Resistance to apoptosis is afforded by inhibitor of apoptosis proteins (IAPs) which bind to and inhibit the caspases responsible for cleavage of substrates leading to apoptotic cell death. Smac (or DIABLO), a proapoptotic protein released from the mitochondrial intermembrane space into the cytosol, promotes apoptosis by binding to IAPs, thus reversing their inhibitory effects on caspases. We have developed a high-throughput fluorescence polarization assay utilizing a fluorescein-labeled peptide similar to the "IAP binding" domain of Smac N terminus complexed with the BIR3 domain of X-linked IAP (XIAP) to identify small-molecule mimics of the action of Smac. The IC(50)s of peptides and a tetrapeptidomimetic homologous to the N terminus of Smac demonstrated the specificity and utility of this assay. We have screened the National Cancer Institute "Training Set" of 230 compounds, with well-defined biological actions, and the "Diversity Set" of 2000 chemically diverse structures for compounds which significantly reduced fluorescence polarization. Highly fluorescing or fluorescence-quenching compounds (false positives) were distinguished from those which interfered with Smac peptide binding to the XIAP-BIR3 in a dose-dependent manner (true positives). This robust assay offers potential for high-throughput screening discovery of novel compounds simulating the action of Smac/DIABLO.     

The Caenorhabditis elegans septin complex is nonpolar

Septins are conserved GTPases that form heteromultimeric complexes and assemble into filaments that play a critical role in cell division and polarity. Results from budding and fission yeast indicate that septin complexes form around a tetrameric core. However, the molecular structure of the core and its influence on the polarity of septin complexes and filaments is poorly defined. The septin complex of the nematode Caenorhabditis elegans is formed entirely by the core septins UNC-59 and UNC-61. We show that UNC-59 and UNC-61 form a dimer of coiled-coil-mediated heterodimers. By electron microscopy, this heterotetramer appears as a linear arrangement of four densities representing the four septin subunits. Fusion of GFP to the N termini of UNC-59 and UNC-61 and subsequent electron microscopic visualization suggests that the sequence of septin subunits is UNC-59/UNC-61/UNC-61/UNC-59. Visualization of GFP extensions fused to the extremity of the C-terminal coiled coils indicates that these extend laterally from the heterotetrameric core. Together, our study establishes that the septin core complex is symmetric, and suggests that septins form nonpolar filaments.     

Degeneration of solventogenic Clostridium strains monitored by Fourier transform infrared spectroscopy of bacterial cells

Strain degeneration in solventogenic clostridia is a known problem in the technical acetone–butanol fermentation bioprocess, especially in the continuous process mode. Clostridial strain degeneration was studied by Fourier transform infrared (FT-IR) spectroscopy of the bacterial cells. Degenerative variant formation in two strains, Clostridium beijerinckii NCIMB 8052 and Clostridium species AA332, was detected spectroscopically. Colonies on solid media were sampled, or assayed directly in situ by IR microscopy. It has previously been shown that the distinctive acidogenic and solventogenic physiological phases of Clostridium acetobutylicum in liquid medium can be discriminated by FT-IR spectroscopy. This was confirmed here for C. beijerinckii NCIMB 8052. The proportion of degenerate cells in a mixed population in liquid medium could be quantified, as the spectral features change in different ways during the normal growth cycle of wild type organisms and degenerate variants in batch culture. This opens a new perspective for physiology-based process monitoring and control, especially of the continuous acetone–butanol fermentation. Journal of Industrial Microbiology & Biotechnology (2001) 27, 314–321. Received 06 October 2000/ Accepted in revised form 20 April 2001