Differential Inhibition of Induced Syntheses of δ-Aminolevulinate Synthetase and Bacteriochlorophyll in Dark-Aerobically Grown Rhodopseudomonas spheroides*

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Abstract
Effects of various factors on the induced syntheses of aminolevuli-nate synthetase, aminolevulinate dehydratase [EC 4.2.1.24] and bacteriochlorophyll in dark-aerobically grown R. spheroides cells were studied. The induced increase of aminolevulinate synthetase was completely inhibited by vigorous aeration and by addition of hemin to the incubation mixtures. Hemin, however, scarcely inhibited the induced synthesis of bacteriochlorophyll. The induced syntheses of aminolevulinate synthetase and bacteriochlorophyll were both strongly inhibited when aminolevulinate was added before the start of incubation. However, when aminolevulinate was added after the commencement of active synthesis of bacteriochlorophyll, the pigment synthesis was not significantly inhibited, in contrast to that the synthesis of aminolevulinate synthetase was immediately and completely inhibited on addition of aminolevulinate. The features of the induced increase of aminolevulinate dehydratase were similar in many respects to those of aminolevulinate synthetase. Omission of iron from the incubation mixtures resulted in nearly complete suppression of bacteriochlorophyll synthesis, but the induction of aminolevulinate synthetase was not suppressed at least in earlier periods of the incubation. Acetate as well as citrate significantly inhibited the bacteriochlorophyll synthesis, but did not inhibit the synthesis of aminolevulinate synthetase. It is suggested that the induced synthesis of aminolevulinate synthetase is not necessarily related to the induced formation of bactcrio-chlorophylL The possible difference between regulatory mechanisms of the induced syntheses of aminolevulinate synthetase and bacteriochlorophyll is discussed.

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