Citric Acid Accumulation Research Articles

Biosynthesis of Citric Acid in Citrus Fruits

NO detailed study has so far been made to find out the mechanism of the formation and accumulation of citric acid in citrus fruits even though studies on the change of acidity and pH during ripening have been reported1. Investigations are in progress in this laboratory to study the biosynthesis of citric acid in citrus fruit (Citrus acida), as a preliminary to which an attempt has been made to locate the stage during the growth of citrus fruit at which citric acid can be detected. The results of the investigation are recorded here.

The nature of the lesion in the succinate-requiring mutants of Neurospora crassa: interaction between carbohydrate and nitrogen metabolism.

SUMMARY: Mutants of Neurospora crassa requiring dicarboxylic acids for an immediate growth response (suc and at suc) oxidize acetate, and are inhibited by fluoroacetate with consequent citric acid accumulation to approximately the same extent as the wild-type. The concentration of nitrogen (as ammonium and nitrate salts) present in the conventional growth medium is inhibitory to the growth of these mutants and leads to an accumulation of aeetylmethylcarbinol, pyruvic acid and α-ketoisovaleric acid. This inhibition is reduced and growth is stimulated by the addition of dicarboxylic acids or by diminution of the nitrogen present in ‘minimal’ medium. The addition of nitrogen salts to suc mutants probably diverts dicarboxylic acids (already in short supply) from the catalysis of the oxidation of C2 fragments via the tricarboxylic acid cycle to other reactions. This effect of nitrogen salts upsets the already precarious dicarboxylic acid balance of the suc mutants leading to a growth requirement and to the accumulation of intermediates.

Induced accumulation of citrate in therapy of experimental lead poisoning.

SummaryThe concept of interference in a metabolic cycle as a means of modifying metal toxicity has been tested. The accumulation of citric acid in certain soft tissues of the rat has been induced by administration of small, non-lethal doses of sodium fluoroacetate. This has been found to give partial protection to rats acutely poisoned with lead nitrate. Of rats given the LD90 of lead nitrate, 53% survived when treated with sodium fluoroacetate. The LD50 of lead nitrate was increased from 58.2 mg/kg (as Pb) in saline controls to 67.7 mg/kg in fluoroacetate-treated rats.

Mechanism of citric acid formation and accumulation in Aspergillus niger

During citric acid accumulation, the specific activity of the condensing enzyme of A. niger increased, whereas isocitric dehydrogenase and aconitase activities were lost. Accumulated citric acid has been shown to inhibit isocitric dehydrogenase even though the mechanism of inhibition has not been clearly understood.

Effect of metabolites on accumulation of citric acid in fluoroacetate-poisoned rats.

SummaryIn fluoroacetate-poisoned rats, the C4 members of the Krebs cycle further increase the accumulation of citrate in the heart but not in the kidney. C2 members in appropriate doses may completely overcome the fluoroacetate block, a finding which may be of significance in antidotal therapy. In non-poisoned rats both C4 and C2 members of the cycle increase the citrate level in the kidney. The bearing of these findings on the metabolic patterns of various organs is discussed.

The Chemical Status of Bean Plants Afflicted with Bicarbonate-Induced Chlorosis

1. The response of bean plants to additions of 8, 16, and 32 m.e./l. NaHCO3 to a base nutrient solution was compared with that of plants grown on base nutrient solution adjusted to pH 8.0 with NaOH. 2. Higher concentrations of sodium bicarbonate were associated with greater intensities of chlorosis and marked inhibition in growth. 3. The treatments primarily effected a lowered iron "activity" and calcium content of the leaves and an enhanced potassium content. 4. The accumulation of citric acid in leaves showing intensified chlorosis was found to be a direct concomitant of potassium content. 5. It is suggested that the primary effect of the bicarbonate ion was through its effect on protoplasmic consistency of the absorbing cells of the roots so that these bean plants showed an accentuated accumulation of monovalent cations and a depressed accumulation of divalent cations. 6. The relation of bicarbonate-induced chlorosis to lime-induced chlorosis in the field is discussed.