Photoinactivation of δ-aminolevulinic acid dehydratase from maize by flavin mononuclotide

The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD -aminolevulinic acid dehydratase - FMN flavin mononucleotide - O₂ ^- superoxide - H₂O₂ hydrogen peroxide - 10₂ singlet oxygen - LA levulinic acid - PBG porphobilinogen - BSA bovine serum albumin - BME 2-mercaptoethanol - SOD superoxide dismutase - pHMB para-hydroxymercuribenzoate - DTT dithiothreitol - FAD flavin adenine dinucleotide - NADH nicotinamide adenine dinucleotide     

Fluidity,permeability and antioxidant behaviour of model membranes incorporated with α-tocopherol and vitamin E acetate

Magnetic resonance studies reveal a marked difference between the binding of α-tocopherol and that of the corresponding acetate (vitamin E acetate) with dipalmitoylphosphatidylcholine (DPPC) vesicles. This is reflected in differences in the phase-transition curves of the DPPC vesicles incorporated with the two compounds, as well as in the ¹³C relaxation times and line widths. A model for the incorporation of these molecules in lipid bilayers has been suggested. α-Tocopherol binds strongly with the lipids, possibly through a hydrogen bond formation between the hydroxyl group of the former and one of the oxygen atoms of the latter. The possibility of such a hydrogen bond formation is excluded in vitamin E acetate, which binds loosely through the normal hydrophobic interaction. The model for lipid-vitamin interaction explains the in vitro decomposition of H₂O₂ by α-tocopherol. α-Tocopherol in conjuction with H₂O₂ can also act as a free-radical scavenger in the lipid phase. The incorporation of α-tocopherol and vitamin E acetate in DPPC vesicles enhances the permeability of lipid bilayers for small molecules such as sodium ascorbate.     

Suppression of Oxygen Evolving System in Spinach Chloroplast Membranes due to Release of Manganese on Exposure to Osmotic Stress in vitro in Presence of Magnesium

When spinach chloroplast membranes were exposed to osmotic stress in vitro, by incubation in 1.0 M sorbitol + 10 mM MgCl₂ their oxygen evolving system was suppressed. The possible reasons for such inactivation of PS II mediated oxygen evolution were examined. There were conformational changes in the chloroplast membranes, as indicated by their absorption spectra. The pattern of sensitivity to DCMU was not altered. The sensitivity of PS II to water stress remained, even after a pre-wash treatment with NaCI (which removed 18 and 24 kD proteins) but not when the thylakoids were pretreated with NH₂0H or CaCl₂ (removed manganese and 33 kD). The manganese content of thylakoid membranes was markedly reduced under osmotic stress in presence of magnesium. We suggest that exposure of chloroplasts to 1.0 M sorbitol in presence of Mg₂₊ released manganese from thylakoid membranes, thereby leading to a suppression in oxygen evolution.     

Antibacterial Compound Isolation and Characterization from the Plant Cynotis axillaris Schult

A novel flavone glycoside was isolated from the methanolic extract of Cynotis axillaris Schult. Various analysis and characterization techniques were used to determine its structure and properties. The compound exhibited a melting point range of 231–232 °C and had a molecular formula of C₂₇H₃₀O₁₄. Several spectral characterization techniques were employed to establish the isolated compound's structure. These included UV-visible spectroscopy, FT-IR, LC-ESI-MS, and NMR spectroscopy. Based on these analyses, the structure of the isolated compound was determined to be 5,7,4’-trihydroxyflavone-8-α-L-rhamnopyranoside-4’-O-β-D-galactopyranosyl. This structure indicates that it is a flavone glycoside consisting of a flavone (5,7,4’-trihydroxyflavone) moiety attached to a sugar molecule (galactopyranosyl) at position 4’, which further bears a rhamnose group at position 8 of the flavone. In addition, to the structural characterization, the compound also demonstrated significant antibacterial efficacy against various bacterial pathogens, including Gram-positive bacteria such as Bacillus subtilis MTCC441 and Gram-negative bacteria such as Escherichia coli MTCC1098, Proteus vulgarize MTCC426, and Salmonella Typhimurium MTCC3224. The antimicrobial activity was evaluated by measuring the zone of inhibition in millimetres, which provides an indication of the compound's ability to inhibit bacterial growth. The study successfully identified and characterized a novel flavone glycoside from Cynotis axillaris Schult. and its antimicrobial activity.     

Improved ethanol tolerance and production in strains of Clostridium thermocellum

Two Clostridium thermocellum strains were improved for ethanol tolerance, to 5% (v/v), by gradual adaptation and mutation. The best mutant gave an ethanol yield of 0.37 g/g substrate, with a growth yield 1.5 times more than its parent. Accumulation of acids and reducing sugars by the mutant strain with 5% (v/v) ethanol was lower than that of the parent strain with 1.5% (v/v) ethanol.     

Epididymal histoplasmosis diagnosed by isolation ofHistoplasma capsulatum from semen

An autochthonous case of epididymal histoplasmosis masquerading as tuberculosis in a 55-year-old male patient is reported from India. It was diagnosed by culture ofHistoplasma capsulatum from semen and by demonstration of the fungus upon re-examination of epididymal biopsy sections previously misinterpreted as tuberculous granuloma. The patient's main complaints were painful epididymal swelling, occasional fever and cough. He was treated successfully by excision of epididymis and vas deferens combined with amphotericin B therapy. This is believed to be the first case of epididymal histoplasmosis to be reported outside the American continent and the fourth of its type reported in the English literature. The case is also noteworthy in thatH. capsulatum was isolated for the first time from semen, and it underlines the importance of mycological culture of semen specimens for diagnosis of genitourinary infections of obscure etiology.Presented at the XII Congress of the International Society for Human and Animal Mycology, Adelaide, Australia, March 13–18, 1994.     

Observations on Schizothrix mexicana Gomont (Cyanophyta) under culture conditions

Using agar gel électrophoresis, the number and relative mobility of seric protein fractions has been determined for twelve species of fishes belonging to the Elasmobranchii, Dipnoi and Actinopterygii.The study of relative mobilities has shown both similitudes and divergences between some of the proteinograms. Immunoelectrophoretic cross tests using the twelve sera and five antisera have shown that these similitudes did not result from protein homology and thus agar gel electrophoresis could not be used to determine phylogenetic relationships between the species considered.

Laboratoire d'Hydrobiologie et de Pisci culture, Université de Kinshasa (Zaïre)     

Inhibition of chlorophyll biosynthesis by α′,α′-dipyridyl during greening of groundnut leaves

The site of inhibition of chlorophyll biosynthesis by α′,α′-dipyridyl was found to be at the level of conversion of chlorophyllide (672 nm) to chlorophyll (678 nm) during greening of groundnut leaves. This inhibition was partially reversed by certain divalent cations.