Pathway for Biodegradation of p-Nitrophenol in a Moraxella sp

A Moraxella strain grew on p-nitrophenol with stoichiometric release of nitrite. During induction of the enzymes for growth on p-nitrophenol, traces of hydroquinone accumulated in the medium. In the presence of 2,2′-dipyridyl, p-nitrophenol was converted stoichiometrically to hydroquinone. Particulate enzymes catalyzed the conversion of p-nitrophenol to hydroquinone in the presence of NADPH and oxygen. Soluble enzymes catalyzed the conversion of hydroquinone to γ-hydroxymuconic semialdehyde, which was identified by high-performance liquid chromatography (HPLC)-mass spectroscopy. Upon addition of catalytic amounts of NAD⁺, γ-hydroxymuconic semialdehyde was converted to β-ketoadipic acid. In the presence of pyruvate and lactic dehydrogenase, substrate amounts of NAD were required and γ-hydroxymuconic semialdehyde was converted to maleylacetic acid, which was identified by HPLC-mass spectroscopy. Similar results were obtained when the reaction was carried out in the presence of potassium ferricyanide. Extracts prepared from p-nitrophenol-growth cells also contained an enzyme that catalyzed the oxidation of 1,2,4-benzenetriol to maleylacetic acid. The enzyme responsible for the oxidation of 1,2,4-benzenetriol was separated from the enzyme responsible for hydroquinone oxidation by DEAE-cellulose chromatography. The results indicate that the pathway for biodegradation of p-nitrophenol involves the initial removal of the nitro group as nitrite and formation of hydroquinone. 1,4-Benzoquinone, a likely intermediate in the initial reaction, was not detected. Hydroquinone is converted to β-ketoadipic acid via γ-hydroxymuconic semialdehyde and maleylacetic acid.     

The photosynthesis of Dunaliella parva Lerche as a function of temperature,light and salinity

The photosynthetic behaviour of Dunaliella parva Lerche from the athalassic lagoon of Fuente de Piedra (Málaga, Southern Spain) was studied experimentally at three NaCl concentrations (1, 2 and 3 M), five temperatures (15, 23, 31, 38 and 42°C) and nine different irradiances between 82 and 891 mol m^–2 s^–1. Results are analyzed to define the best growing conditions for the algae. D. parva shows the highest photosynthetic rates at a NaCl molarity of 2 M, under a moderate light intensity (600 mol m^–2 s^–1) at 31°C. Above this light intensity a clear photoinhibition of the photosynthesis was found at 2 M and 3 M of NaCl. D. parva is a halotolerant and a thermoresistant species as evidenced by its net photosynthesis rate and positive values of oxygen evolution at 42°C.Two methods for modelling photosynthesis vs. irradiance curves are discussed. The first is a single model, based on third-order polynomial equations, and the second is double model, based on hyperbolical Michaelis-Menten type functions and negative exponential to define photoinhibition.     

Juvenile hormone and photoperiodically controlled polymorphism in Aphis fabae: Postnatal effects on presumptive gynoparae

Long days (short nights) (LD 16:8) and high temperatures (> 15°C) have an apterizing effect on the short day (LD 12:12) induced, presumptive gynopara of Aphis fabae. Transfer of presumptive gynoparae to long days (15°C) or to 25°C (short days) at varying times during postnatal development demonstrate that the adult form is determined by the second day of the second instar, i.e. 5 days after birth at 15°C. Transfer on day 1 induces maximum apterization with the proportion of aphids affected decreasing with age at transfer.Apterization induced by long days immediately after birth can, to some extent, be cancelled by return to short days but only up to day 4. Thus long days are morphogenetically more potent than short days at the beginning of larval development. At temperatures above 15°C the proportion of aphids apterized increases almost linearly.Apterized insects can be distinguished from juvenilized insects in the fifth-instar. Topical application of juvenile hormone (JH) induces both apterization and juvenilization of presumptive gynoparae but at different times during larval development, JH treatment during the early-instars promotes apterization but induces little juvenilization, whereas maximum juvenilization, without apterization, is produced by middle-instar treatment. The apterizing effects of JH are, thus, not due to its neotenic action.The response profile of JH-induced apterization is similar to that observed with long days and 25°C. It is suggested that such conditions increase endogenous JH levels in A. fabae. The three naturally occurring JH's differ in activity in the order JH I > JH II > JH III. Both long-day and JH-apterized insects switch from the normal ovipara production of the adult gynopara to vivipara production.     

Survival of Paracoccidioides brasiliensis yeast cells under microaerophilic conditions

The ability of P. brasiliensis yeast cells to withstand microaerophilic conditions was investigated in a liquid medium distributed in tall columns in screw-capped tubes. Young cells of three isolates were inoculated on top of the medium, and the tubes were incubated aerobically and anaerobically at 36 degrees C for 28 days. The viability of cells that had sedimented to the bottoms of the tubes was studied by fluorescent microscopy and by their capacity to resume growth when transferred to fresh medium under continuous agitation. The proportion of viable cells in the sediments diminished with time of incubation. However, after 28 days, 27% of the cells were still viable and fully capable of active growth when placed under adequate aeration. On the other hand, drastic reduction of oxygen access elicited an accelerated death rate, with no survival after 7 days of incubation.     

Deacetylation of N8-acetylspermidine by subcellular fractions of rat tissue

The in vitro deacetylation of N⁸-acetylspermidine by an enzyme activity in rat tissues is described. This deacetylase activity occurs as a soluble, cytoplasmic enzyme in rat liver and was detected in the 100,000g supernatant fraction of all tissues examined. The highest specific activity was found in liver. Spleen, kidney, and lung were found to contain 20–50% of the activity in liver, while heart, brain, and skeletal muscle exhibited from 2 to 10% of the activity in liver. Serum contained only barely detectable levels of activity, much lower than any of the tissues studied. The in vitro metabolism of N¹-acetylspermidine differed from that observed for N⁸-acetylspermidine and does not appear to involve a simple deacetylation reaction.     

Studies on the mode of action of hygromycin B, an inhibitor of translocation in eukaryotes.

Hygromycin B is an unusual aminoglycoside antibiotic active against both prokaryotic and eukaryotic cells. Hygromycin B at 0.38 mM concentration completely halts yeast cell growth in rich media, presumably by preventing protein synthesis by cytoplasmic ribosomes. Polypeptide synthesis in cell-free extracts from rabbit reticulocytes, wheat germ and yeast is strongly blocked by low concentrations of hygromycin B. The antibiotic inhibits peptide chain elongation by yeast polysomes by preventing elongation factor EF-2-dependent translocation, although it does not affect either the formation of the EF-2-GTP-ribosome complex or the EF-2- and ribosome-dependent GTP hydrolysis which takes place uncoupled from translocation. The inhibition of translocation by hygromycin B might result from the stabilization of peptidyl-tRNA bound to the ribosomal acceptor site, since the stability of [3H]Phe-tRNA-EF-1-poly(U)-ribosome and [3H]Phe-tRNA-poly(U)-ribosome complexes is increased in the presence of hygromycin B. The inhibition of polyphenylalanine synthesis by reticulocyte ribosomes and enzymic translocation of peptidyl-tRNA by yeast polysomes can be reversed by increasing concentrations of EF-2 suggesting a relationship between the binding sites of EF-2 and hygromycin B on the ribosome. Neither non-enzymic translocation, that takes place in the presence of high potassium concentrations, nor the peptide bondforming step are affected by hygromycin B.     

Effect of fasting and insulin on the glucagon-induced orthophosphate incorporation to the isolated perfused rat liver.

Isolated perfused fed rat livers spontaneously liberated glucose and orthophosphate to the medium; 24-hr fasted rat livers did not exhibit these phenomena. In perfused fed rat livers, glucagon (2 mug) increased glucose output and promoted orthophosphate incorporation. In perfused fed rat livers, insulin (250 or 500 mU) inhibited the spontaneous liberation of glucose and orthophosphate. Comparable doses of insulin significantly reduced the glucagon (2 mug)-induced increase in glucose output from perfused fed rat liver, but did not affect orthophosphate uptake by the organ.