Change of Metabolic Stability of Δ-Aminolevulinate Synthetase in Rhodopseudomonas spheroides Cells Probably Related to Changes of Intracellular Oxidation-Reduction State

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Abstract
The level of δ-aminolevulinate (ALA) synthetase in Rhodopseudomonas spheroides cells grown anaerobically in the light or grown aerobically in the dark and in which the enzyme had been induced by poor aeration decreased rapidly and extensively on aeration of the medium or addition of chloramphenicol or puromycin. The level of ALA dehydratasc [EC 4.2.1.24] also decreased under these conditions to a lesser extent. The ALA synthetase level in cells grown in the light also decreased under brighter light (6500 lux) even under anaerobic conditions. The extensive decrease in ALA synthetase activity could not be accounted for by its dilution due to cell proliferation, but seemed to represent actually decrease in the amount of enzyme or irreversible inactivation of the enzyme in the cells. In contrast, the ALA synthetase level in cells grown aerobically in the dark and in which the enzyme had not been induced was not affected at all by either vigorous aeration or inhibitors of protein synthesis. Evidence was obtained suggesting that extracts of cells grown in the light or those in which enzyme had been induced contain two types of ALA synthetase with different stabilities with respect to temperature and storage. In contrast extracts of cells grown in the dark in which enzyme has not been induced contain only one type of enzyme which is relatively stable. The levels of succinyl-CoA synthetase [EC 6.2.1.4] and ribulose-l, 5-diphosphate carboxylase [EC 4.1.1.39] in these cells did not decrease significantly on changing the incubation conditions or adding inhibitors of protein synthesis. It was concluded that the ALA synthetases in cells grown in the light or in which enzyme has been induced are metabolically unstable and the stability of ALA synthetase in vivo is markedly affected by change in the intracellular oxidation-reduction state to a more oxidized state.

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