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[Nitrates and nitrites in plants].

The formation of aminoacids and proteins from the nitrogen which enters the roots as nitra t involves a complex reaction requiring energy. The first step requires a metalloflavoprotein, the nitrate reductase and the successive intervention of NADPH, FAD and reduced molybdenum which transfers electrons to nitrate and reduces it to nitrite. The following steps involve NADPH, FAD, Copper, Iron and Manganese, the last steps of the successive reductions being ammonia, needed for the aminoacids synthesis. The activity of the different enzymes are under the dependence of the genetic equipment of the plant, of the nitrogen and oligo-element nutrition and of the different factors acting on the photosynthesis.

Amino Acids↗

[Content of nicotinamide coenzymes in rat liver under conditions of nicotinamide administration].

The content of NAD+, NADH, NADP+, NADPH in the liver of normal, fasting rats, those on the low-carbohydrate diet and suffering from alloxan diabetes was studied as affected by nictotinamide. Changes in the NAD+ content, sum of nicotinamide coenzymes, the [NAD+] + [NADP+]/[NADH] +/- [NADPH] and [NAD+] + [NADH] (sum of nicotinamide coenzymes) ratios are mainly due to nicotinamide administration. Changes in the content of reduced forms of both nucleotides depend equally on nicotinamide administration and the physiological state of animals. Response of the rat organism to nicotinamide administration consists in a sharp intensification of NAD+ synthesis and in a less pronounced intensification of NADH, NADP+ and NADPH synthesis.

Animals↗

Determination of the molar absorptivity of NADH.

The molar absorptivity of NADH at 340 nm has been determined by an indirect procedure in which high-purity glucose is phosphorylated by ATP in the presence of hexokinase, coupled to oxidation of the glucose-6-phosphate by NAD+ in the presence of glucose-6-phosphate dehydrogenase. The average value from 85 independent determinations is 6317 liter mol-1 cm-1 at 25 degrees C and pH 7.8. The overall uncertainty is -4.0 to +5.5 ppt (6292 to 6352 liter mol-1 cm-1), based on a standard error of the mean of 0.48 ppt and an estimate of systematic error of -2.6 to +4.1 ppt. Effects of pH, buffer, and temperature on the molar absorptivity are also reported.

Absorption↗

Copper catalyzed alkaline autoxidation of selenocystamine.

In alkaline medium and in the presence of cupric ions selenocystamine undergoes autoxidation and is entirely transformed into selenohypotaurine. Among the different metal ions tested, Fe, Co, Ni, Cu, Ag, Mg, Mn, only cupric ions are effective in catalyzing the reaction. The reaction shows an optimum around pH 13. In most respects the autoxidation of selenocystamine is similar to the alkaline autoxidation of cystamine. Some data on the paper and ion exchange chromatographic behaviour of selenohypotaurine and selenotaurine are reported, as also details for the synthesis of selenotaurine.

Cations, Divalent↗

Autooxidation and hydroxylation reactions of oxygenated cytochrome P-450cam.

Oxy-ferrous substrate-bound cytochrome P-450cam (mrsO2) autooxidizes in the absence of its specific effector protein, putidaredoxin, without hydroxylating the substrate, camphor. The autooxidation is first order with an activation energy of 17 kcal mol-1 at 25 degrees, pH 7.0. Substrate removal and low pH accelerate the reaction. The product, 5-exo-OH camphor, and a nonhydroxylated pseudosubstrate, norcamphor, stabilize the complex in a manner similar to camphor. Increased oxidation rate of mrsO2 and substrate hydroxylation are induced by putidaredoxin, rebredoxin, cytochrome b5, and the apoproteins of the latter two. Dihydrolipoic acid and other dithiols also replace putidaredoxin as effector molecules, but 1000-fold higher concentrations are required. Effector molecules do not increase the autooxidation rate of mrsO2 unless camphor, norcamphor, or another pseudosubstrate is present. Kinetic evidence is presented showing that an active complex between mrsO2 and effector is a required intermediate in mixed function oxidation.

Animals↗

[Photoinduced reduction of NAD(P) in the cells of green sulfur bacteria].

The spectrum of a photoinduced increase in luminescence of the cells of the gree sulphur bacterium Chlorobium limicola f. thiosulfatophilum, within the range of 400 to 520 nm, was found to correspond to the spectrum of luminescence of NADH in the protein-bound form. Photoinduced reduction of NAD(P) in green bacteria, contrary to purple bacteria, is not susceptible to the action of p-chlorocarbonylcyanide phenlhydrazone which uncouples photophosphorylation. Therefore, in Chlorobium limicola f. thiosulfatophilum, NAD(P) is reduced by direct non-cyclic transport of electrons via the photosynthetic chain. NAD(P)H is utilized mainly in the system of CO2 fixation; the process is inhibited by fluoroacetate, and the inhibition is eliminated by substrates of the cycle of carboxylic acids.

Carbon Dioxide↗

[Changes in oxidative systems of liver microsomes in rats following a single administration of phenobarbital and morphine].

During the first three hours after a single administration of phenobarbital or morphine into rats a marked increase was observed in the activity and content of the respiratory chain components responsible for the oxidation of NAD-H2 and NADP-H2 in liver microsomes. This activation of oxidative enzymes correlated with the disappearance of hypnotic and analgetic effects of the narcotics. The phase following the normalization of oxydative systems was characterized by the increase of microsomal enzymes level. This is related to their specific induction only by phenobarbital.

Animals↗

[Ferrous ion oxidation and uranium solubilization from a lowgrade ore by "Thiobacillus ferrooxidans" (author's transl)].

The microbiological oxidation of ferrous ion and the extraction of uranium from a low-grade ore has been studied using an adapted strain of Thiobacillus ferrooxidans. The effect of temperature, pH, volumetric oxygen transfer coefficient, K1a, and aeration number, Ia, on the activity of the microorganism has been determined. The activation energy for ferrous iron oxidation was calculated to be - 13.9 +/- 0.1 kcal/mole and inactivation (thermal death of bacteria) 53.3 +/- 0.2 kcal/mole. Temperature coefficient, Q10, was estimated to be 1.8. Uranium extraction varied between 80 and 100%.

Hydrogen-Ion Concentration↗

Hydrogen exchange at the amide group of reduced pyridine nucleotides and the inhibition of that reaction by dehydrogenases.

Stopped flow ultraviolet spectroscopy has been used to measure the rate of hydrogen exchange with solvent at the amide group of reduced nicotinamide nucleotide coenzymes. Several mechanisms for the exchange reaction are considered in the light of the kinetic data. Complex formation between the coenzyme and any of four dehydrogenases markedly slows the rate of hydrogen exchange. Hydrogen bond formation and/or hydrophobic interactions within these complexes are thought to be the reasons for the decreased rate of exchange.

Alcohol Oxidoreductases↗

The metabolic activation of the carcinogen 1'-hydroxysafrole in vivo and in vitro and the electrophilic reactivities of possible ultimate carcinogens.

Administration of [2',3'-3H]-1'-hydroxysafrole to rats or mice resulted in the formation of hepatic DNA-, ribosomal RNA-, and protein-bound 3H derivatives. Alkaline digestion of the 3H-protein released 0.1 to 0.3% of the 3H as a derivative that was identified as 3'-methylmercaptoisosafrole by its cochromatography in five solvent systems with the synthetic compound. 1'-Hydroxysafrole was metabolized at a low rate by rat and mouse liver cytosols in a 3'-phosphoadenosine 5'-phosphosulfate-dependent reaction to a derivative (presumably the sulfuric acid ester) that was captured by its reaction with RNA. Likewise, 1'-hydroxysafrole was oxidized at a low rate by rat and mouse liver microsomes to 1'-hydroxysafrole-2',3'-oxide in a reduced nicotinamide adenine dinucleotide phosphate-dependent reaction. Both of these electrophilic metabolites are candidate ultimate carcinogenic derivatives of 1'-hydroxysafrole. The electrophilic reactivities of various safrole derivatives with nucleosides were determined to be in the order of 1'-oxosafrole greater than 1'-acetoxysafrole greater than 1'-acetoxysafrole-2',3'-oxide greater than 1'-hydroxysafrole-2',3'-oxide greater than safrole-2',3'-oxide greater than or equal to 1'-oxosafrole-2',3'-oxide. The major reactions were generally observed with guanosine. A major reaction product of 1'-acetoxysafrole and guanosine 5'-monophosphate yielded 3'-hydroxyisosafrole under very mild acidic conditions. These data further substantiate the previous characterization of this reaction product as O-6-(isosafrol-3'-yl)guanylic acid. The syntheses of 1'-oxosafrole, 2',3'-dehydrosafrole, [2',3'-3H]-1'-hydroxysafrole, and the 2',3'-oxed.

Acetyltransferases↗

[Disadvantages of acid precipitation of proteins during the assay of blood glucose by the enzymatic glucose oxidase-peroxidase system].

In the enzymatic procedure for blood sugar by means of glucose oxidase, acid protein precipitation of blood by perchloric acid or trichloracetic acid liberated oxidizing substances, which enhanced the coloration density in oxidizing the reduced chromogen of the reaction mixture, independently of the hydrogen peroxide generated from glucose, and would give false high values of glycemia, if additional precautions had not been taken. These substances, increasing considerably with times and temperature of blood conservation, would be of peroxide nature, and would accumulate in red blood cells during their exposure to air.

Animals↗