Biochimica et biophysica acta最新文献

The following sequence of metabolic reactions has been proved by chemical methods to occur in resting cells of acid-fast bacteria: p-aminobenzoic acid → p-aminobenzyl alcohol → p-hydroxyaniline. The first step in this sequence has been demonstrated to be a direct enzymatic reduction by using both ring- and carboxy-¹⁴C-labeled p-aminobenzoic acid. A synthetic route, which should be of general use, was employed to convert [¹⁴C]aniline to ring-¹⁴C-labeled p-aminobenzoic acid. It is suggested that the unique transformation of p-aminobenzyl alcohol to p-hydroxyaniline may be a specific case of a more general mechanism involved in enzymatic hydroxylation of aryl compounds.

Ascorbic acid has been found to induce the fluorescence of an intermediate oxidation product of noradrenaline which is formed in a ferricyanide oxidation. The fluorescence of the product is a function of the ascorbic acid and noradrenaline concentration and at conditions at which the fluorescence of the noradrenaline product is optimal the fluorescence of adrenaline, tested similarly, in negligible. The reaction has a definite pH optimum (pH 6) and the fluorescence of the final product depends on the time of the oxidation. The stability and rate of formation of the noradrenaline product is dependent upon the concentration level of the ascorbic acid and ferricyanide. The reaction shows promise as the basis for a new noradrenaline assay.

The influence of the external Na⁺ and K⁺ concentration and of ouabain on I⁻ uptake and release was studied in cow-thyroid slices blocked with propylthiouracil. It could be shown that the I⁻ transport is dependent on the presence of both Na⁺ and K⁺ ions. However, the dependence on Na⁺ seems to be more direct: the effect of removal of K⁺ and of the application of ouabain set in only after a latency period while the effect of Na⁺ removal was immediate. The half-time of I⁻ release due to removal of Na⁺ from the medium was markedly shorter than that due to K⁺ removal or that of the release caused by ouabain. However, the half-times in the latter two cases were similar. A thyroid slice kept for a long time under ouabain poisoning in a solution wherein 90% of the Na⁺ was replaced by Li⁺ was still able to accumulate I⁻ for a short time when brought back into a medium of normal Na⁺ content in spite of the uninterrupted presence of ouabain. The possible connections between the K⁺-Na⁺ transport mechanism and the I⁻ transport are discussed.

In principle two basically different relations can be thought of. Either the I⁻ transport is directly coupled with the Na⁺K⁺ exchange mechanism or the cation-concentration differences created by the Na⁺K⁺ transport system are a prerequisite for the I⁻ transport. The present results are taken to favour the latter assumption.

• 1.

  1. An enzyme which catalyses the transamination between γ-hydroxyglutamate and α-ketoglutarate was extracted from rat-liver acetone powder and purified in excess of 15-fold. Fractionation of the enzyme from a separate aspartate transaminase (L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1) remained incomplete.

• 2.

  2. [2-¹⁴C]Pyruvate was incorporated into γ-hydroxy-α-ketoglutarate and γ-hydroxyglutamate in the presence of glyoxylate in rat-liver homogenate. Specific activity values of these three compounds indicated the occurence of the following pathway: Pyruvate + glyoxylate ⇌ γ-hydroxy-α-ketoglutarate ⇌ γ-hydroxyglutamate.

• 3.

  3. A further possible pathway of γ-hydroxy-α-ketoglutarate metabolism leading to malate and of γ-hydroxyglutamate to its decarboxylation product or to L-hydroxyproline were inferred and discussed.