A Novel Class of Herbicides (Specific Inhibitors of Imidazoleglycerol Phosphate Dehydratase)

A new mode of herbicidal action was established by finding specific inhibitors of imidazoleglycerol phosphate dehydratase, an enzyme of histidine (His) biosynthesis. Three triazole phosphonates inhibited the reaction of the enzyme with Ki values of 40 [plus or minus] 6.5, 10 [plus or minus] 1.6, and 8.5 [plus or minus] 1.4 nM, respectively, and were highly cytotoxic to cultured plant cells. This effect was completely reversed by the addition of His, proving that the cytotoxicity was primarily caused by the inhibition of His biosynthesis. These inhibitors showed wide-spectrum, postemergent herbicidal activity at application rates ranging from 0.05 to 2 kg/ha.     

Plant regeneration from protoplasts of Gentiana by embedding protoplasts in gellan gum

A protoplast-to-plant system was developed in Gentiana using a gellan gum-embedding culture. Viable protoplasts could be routinely isolated from in vitro-grown plantlets, and they were embedded in 0.2% gellan gum-solidified B5 medium containing 2 mg l^-1 NAA, 0.1 mg l^-1 TDZ, 0.1 M sucrose and 0.4 M mannitol. Weekly addition of fresh liquid medium was essential for preventing cell browning. Colony growth was promoted by lowering mannitol concentration of the culture media after one month, and visible colonies were produced after 2 months of culture. Shoot regeneration from protoplast-derived calluses was stimulated by 1 to 10 mg l^-1 TDZ in combination with 0.1 mg l^-1 NAA. Protoplast-derived plants were recovered following rooting of the shoots in plant growth regulator-free medium and they were successfully transferred to soil.Abbreviations BA benzylaminopurine - FDA fluorescein diacetate - FW fresh weight - MES 2-N-morpholinoethane sulfonic acid - NAA -naphthaleneacetic acid - TDZ N-1,2,3-thiadiazol-5-yl-N-phenylurea (also called thidiazuron)     

Immunocytochemical localization of thrombomodulin in the aqueous humor passage of the rat eye

 This report describes the distribution and localization of thrombomodulin (TM) in the rat eye by light and electron microscopic immunocytochemistry. In addition to the endothelium of the entire vasculature, TM was found on the non-vascular structures lining the cavities of the posterior and anterior chambers and the limbus. TM was localized on the basal, lateral, and apical plasma membranes of the inner and outer ciliary epithelium, and the posterior iris epithelium in which there was no polarized expression of TM. In the anterior chamber, TM was localized on the luminal surface of the corneal endothelium, but was negative on the anterior border layer of the iris, which is composed of a discontinuous layer of fibroblasts and collagen fibers. Thus, TM was present at sites of cell-to-cell contact. TM was also present on the endothelia of the trabecular meshwork and the Schlemm’s canal in the limbus. TM was localized not only on the luminal plasma membrane, but also on the cytoplasmic giant vacuoles in the endothelial cells of the Schlemm’s canal. These findings extend the importance of anticoagulant mechanisms to the systems of secretion, circulation, and drainage of the aqueous humor. Accepted: 18 March 1997     

Importance of Fe2+-ADP and the relative unimportance of OH in the mechanism of mitomycin C-induced lipid peroxidation

The mechanism of mitomycin C-induced lipid peroxidation has been studied at pH 7.5, using systems containing phospholipid membranes (liposomes) and an Fe3+-ADP complex with purified NADPH-cytochrome P-450 reductase. Both O2- and H2O2 are generated during the aerobic enzyme-catalyzed reaction in the presence of mitomycin C. Hydroxyl radical is formed in the reaction by the reduction of H2O2. This is catalyzed by the Fe2+-ADP complex in a phosphate buffer or to a lesser extent when in a Tris-HCl buffer. The reduction of Fe3+-ADP to Fe2+-ADP is mainly achieved by O2-. The resulting Fe2+-ADP in the presence of O2 forms a perferryl ion complex which is a powerful stimulator of lipid peroxidation. However, the formation of such an iron-oxygen complex is strongly inhibited by phosphate ions, which do not interfere with the generation of OH radicals. These findings suggest that, since lipid peroxidation occurs in a Tris-HCl buffer (but not in a phosphate buffer), the OH radical is unlikely to be involved in the observed lipid peroxidation process.     

Inhibition of indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase by β-carboline and indole derivatives

β-Carboline derivatives inhibited both indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase activities from various sources. Among them, norharman is most potent for both enzymes from mammalian sources. Kinetic studies revealed that norharman is uncompetitive (K_i = 0.12 mm) with l-tryptophan for rabbit intestinal indoleamine 2,3-dioxygenase, and linearly competitive (K_i = 0.29 mm) with l-tryptophan for mouse liver tryptophan 2,3-dioxygenase. In addition, some β-carbolines selectively inhibited one enzyme or the other. Pseudomonad tryptophan 2,3-dioxygenase was inhibited by a different spectrum of β-carbolines. Such a selective inhibition by the structure of substrate analogs is more evident by the use of indole derivatives. Indole-3-acetamide, indole-3-acetonitrile and indole-3-acrylic acid exhibited a potent inhibition for mammalian tryptophan 2,3-dioxygenase, while they moderately inhibited the pseudomonad enzyme. However, they showed no inhibition for indoleamine 2,3-dioxygenase. These results suggest the difference of the structures of the active sites among these enzymes from various sources.     

Predominance of beta-structure in solubilized zona pellucida from porcine ova

The isolated zona pellucida from porcine ova was effectively solubilized in water at 60 degrees C within one hour. The circular dichroic spectra of zona in water with and without dithiothreitol showed the beta-form. Although sodium dodecyl sulfate partially induced helical structure, the beta-form was considerably retained. These results indicate that the zona glycoproteins have a structure-forming potential for the beta-structure and the hydrogen bonds of the beta-structure stabilize the supramolecular complex of the zona pellucida. The beta-form was also detected in zona solubilized by tryptic digestion. Porcine acrosin, however, did not solubilize the zona.