Reduction of 4-androstene-3,17-dione by growing cucumber plants

4-[4-¹⁴C]Androstene-3,17-dione was applied to the leaves of growing cucumber plants, Cucumis sativus, twice a week. Four weeks after the first     

Prolactin,hypercalcemia and corpuscles of stannius in seawater eels

In intact eels in sea water (SW), ovine prolactin (PRL) treatment induces hypercalcemia, but its mechanism of action, which is discussed, remains to be defined. Corpuscles of Stannius (CSt) are modified simultaneously: two cell categories then become evident. The first cell type (type 1) predominates; it has an oval shape and large granules, it shows a nuclear and nucleolar hypertrophy and a mitotic activity, and appears greatly stimulated by PRL; it may elaborate a hypocalcemic factor (hypocalcin) which would compensate for the PRL-induced hypercalcemia. A similar effect, although slightly less intense, is detected in hypophysectomized-PRL treated eels in SW. A second cell type (type 2), is more elongated, smaller in size, and has an oval nucleus and fine granules. Scarcely less active in SW, it is significantly stimulated by PRL despite an increased blood sodium and potassium level. This experiment does not help to clarify its function.     

The effect of pyrazines on the metabolism of tryptophan and nicotinamide adenine dinucleotide in the rat Evidence of the formation of a potent inhibitor of aminocarboxy-muconate-semialdehyde decarboxylase from pyrazinamide

The intraperitoneal or oral administration of pyrazinamide and pyrazinoic acid (pyrazine 2-carboxylic acid) resulted in a marked increase of the NAD content in rat liver. The injections of pyrazine and pyrazine 2,3-dicarboxylic acid exhibited no significant effect on the hepatic NAD content. The boiled extract obtained from liver and kidney of rat injected with either pyrazinamide or pyrazinoic acid exhibited a potent inhibitory effect on the aminocarboxymuconate-semialdehyde decarboxylase (EC 4.1.1.45) activity in either liver or kidney, although pyrazinamide or pyrazinoic acid per se did not inhibit the enzyme activity. The unknown inhibitor of aminocarboxymuconate-semialdehyde decarboxylase was dialysable and heat-stable, and mostly excreted in urine by 6 and 12 h after injection of pyrazinoic acid and pyrazinamide, respectively. Pyrazine 2,3-dicarboxylic acid, pyrazine, nicotinamide, nicotinic acid, tryptophan, anthranilic acid, 5-hydroxyanthranilic acid and quinolinic acid exhibited no significant effect on the aminocarboxymuconate-semialdehyde decarboxylase activity in liver and kidney at the concentration of 1 mM in the reaction mixture. The expired ¹⁴CO₂ from l-[benzen ring-U-¹⁴C]tryptophan was markedly decreased by the pyrazinamide injection, while the urinary excretion of ¹⁴C-labeled metabolites from l-tryptophan, mainly quinolinic acid, was markedly increased. These results suggest that the glutarate pathway of l-tryptophan was strongly inhibited by the inhibitor produced after the administration of pyrazinoic acid and pyrazinamide. Pyrazinamide but not pyrazinoic acid also exhibited a significant inhibition of the nuclear enzyme poly(ADP-ribose) synthetase in rat liver.     

Type I Antifreeze Proteins Enhance Ice Nucleation above Certain Concentrations

In this study, we examined the effects that antifreeze proteins have on the supercooling and ice-nucleating abilities of aqueous solutions. Very little information on such nucleation currently exists. Using an automated lag time apparatus and a new analysis, we show several dilution series of Type I antifreeze proteins. Our results indicate that, above a concentration of ∼8 mg/ml, ice nucleation is enhanced rather than hindered. We discuss this unexpected result and present a new hypothesis outlining three components of polar fish blood that we believe affect its solution properties in certain situations.     

Effect of phenylhydrazine on red blood cell metabolism

In addition to the well known effect of phenylhydrazine on red blood cells (methaemoglobin and Heinz body formation, autologous IgG binding, lipid peroxidation, etc.) an increased glucose utilization was observed. Measurement of 14CO2 formation from [1-14C]-glucose showed a maximum value at 2mM phenylhydrazine followed by a progressive inhibition on increasing the drug concentration to 16 mM. Concomitantly we found a reduction in the reduced glutathione concentration but not a corresponding increase in the level of oxidized glutathione. Phenylhydrazine also causes ATP depletion. The ATP is in part dephosphorylated to ADP and AMP and in part converted to inosine monophosphate and hypoxanthine. Measurement of the cell content of reduced and oxidized pyridine nucleotides was also performed and showed a progressive increase in the reduced forms of these coenzymes. Thus phenylhydrazine promotes cellular ATP depletion followed by adenine nucleotide catabolism that is not efficiently counteracted by an increase in glucose utilization. The relevance of these data to the mechanism of phenylhydrazine-induced anemia is discussed.     

Regulation of enzymes and isoenzymes of carbohydrate metabolism in the yeast Saccharomyces cerevisiae

An electrophoretic method has been devised to investigate the changes in the enzymes and isoenzymes of carbohydrate metabolism, upon adding glucose to derepressed yeast cell. (i) Of the glycolytic enzymes tested, enolase II, pyruvate kinase and pyruvate decarboxylase were markedly increased. This increase was accompanied by an overall increase in glycolytic activity and was prevented by cycloheximide, an inhibitor of protein synthesis. (ii) In contrast, respiratory activity decreased after adding glucose. This decrease was clearly shown to be the result of repression of respiratory enzymes. A rapid decrease within a few minutes of adding glucose, by analogy with the so-called ‘Crabtree effect’, was not observed in yeast. (iii) The gluconeogenic enzymes, fructose-1,6-bisphosphatase and malate dehydrogenase, which are inactivated after adding glucose, showed no significant changes in electrophoretic mobilities. Hence, there was no evidence of enzyme modifications, which were postulated as initiating degradation. However, it was possible to investigate cytoplasmic and mitochondrial malate dehydrogenase isoenzymes separately. Synthesis of the mitochondrial isoenzyme was repressed, whereas only cytoplasmic malate hydrogenase was subject to glucose inactivation.     

The relationship of 4-aminobutyric acid metabolism to ammoniagenesis in renal cortex

Mitochondrial 4-aminobutyrate aminotransferase in rat kidney can utilize pyruvate as the acceptor for the amino group of 4-aminobutyrate. Renal 4-aminobutyrate aminotransferase activity at saturating equimolar concentration of 4-aminobutyrate and 5 mM pyruvate is 42.8 ± 2.5 μmol/g protein per h (mean ± S.E.M.) or 70% of 4-aminobutyrate aminotransferase activity with equimolar α-ketoglutarate. 4-Aminobutyrate aminotransferase in brain does not transaminate with pyruvate. Since pyruvate is an important mitochondrial metabolite in kidney, net disposal of glutamate via the 4-aminobutyrate pathway is possible. The renal 4-aminobutyrate pathway in the rat has other distinctive features when compared with the pathway in rat brain. Most inhibitors of rat neuronal glutamate decarboxylase were ineffective against the renal form of the enzyme, but 20 mM semicarbazide inhibited the latter form by 80% (P < 0.001) in vitro and reduced renal 4-aminobutyrate content by 75% (P < 0.001) in vivo. In the presence of 20 mM semicarbazide, ammoniagenesis by rat renal cortex slices incubated in 1 mM glutamine was inhibited 26% (P < 0.01). Semicarbazide was proportionately less effective (15% inhibition) when ammoniagenesis was stimulated (+243%) in slices prepared from chronically acidotic animals, and was no deterrant to ammoniagenesis when non-acidotic slices were incubated in supraphysiologic concentrations of 10 mM glutamine. We conclude that whereas integrity of the renal 4-aminobutyrate pathway may contribute to glutamate disposal and thus ammoniagenesis under physiologic conditions, the pathway is a passive participant in the overall process of ammoniagenesis.