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Tyramine oxidase in Klebsiella aerogenes is highly specific for tyramine, dopamine, octopamine, and norepinephrine, and its synthesis is induced specifically by these compounds. The enzyme is present in a membrane-bound form. The Km value for tyramine is 9 X 10(-4) M. Tyramine oxidase synthesis was subjected to catabolite repression by glucose in the presence of ammonium salts. Addition of cyclic adenosine 3',5'-monophosphate (cAMP) overcame the catabolite repression. A mutant strain, K711, which can produce a high level of beta-galactosidase in the presence of glucose and ammonium chloride, can also synthesize tyramine oxidase and histidase in the presence of inducer in glucose ammonium medium. Catabolite repression of tyramine oxidase synthesis was relieved when the cells were grown under conditions of nitrogen limitation, whereas beta-galactosidase was strongly repressed under these conditions. A cAMP-requiring mutant, MK54, synthesized tyramine oxidase rapidly when tyramine was used as the sole source of nitrogen in the absence of cAMP. However, a glutamine synthetase-constitutive mutant, MK94, failed to synthesize tyramine oxidase in the presence of glucose and ammonium chloride, although it synthesized histidase rapidly under these conditions. These results suggest that catabolite repression of tyramine oxidase synthesis in K. aerogenes is regulated by the intracellular level of cAMP and an unknown cytoplasmic factor that acts independently of cAMP and is formed under conditions of nitrogen limitation.

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In Klebsiella aerogenes, arylsulfatase synthesis was repressed by inorganic sulfate, sulfite, sulfide, thiosulfate, and cysteine, but not by methionine under normal growth conditions. We isolated cysteine-requiring mutants (Cys-), and mutants (AtsS-, AtsR-) in which the regulation of arylsulfatase synthesis was altered. In the cysteine auxotroph, enzyme synthesis was also repressed by inorganic sulfate or cysteine. Kinetic studies on mutants of the cysteine auxotroph showed that inorganic sulfate repressed arylsulfatase synthesis and that this was not due to cysteine formed by reduction of sulfate. Arylsulfatase synthesis in the AtsSmutant was not repressed by inorganic sulfate but was repressed by cysteine. This mutant strain had a normal level of inorganic sulfate transport. Another mutant strain, defective in the inorganic sulfate transport system, synthesized arylsulfatase in the presence of inorganic sulfate but not in the presence of cysteine. The AtsSmutant could synthesize the enzyme in the presence of inorganic sulfate but not cysteine. The AtsRmutant could synthesize the enzyme in the presence of either inorganic sulfate or cysteine. These results suggest that there are two independent functional corepressors of arylsulfatase synthesis in K. aerogenes. Harada and Spencer (8) showed that, in many fungi, arylsulfatase synthesis is inhibited by the presence of sulfur compounds, such as sulfate, sulfite, thiosulfate, and cysteine, which are thought to be direct intermediates in the assimilation of sulfate, but that it is not inhibited by compounds such as methionine, taurine, and cysteate, which are not direct intermediates. A similar division of sulfur sources was observed in the arylsulfatase synthesis of Aerobacter aerogenes (9). The effects of various sulfur compounds in repressing arylsulfatase synthesis has been thought to be due to conversion of these compounds to a single corepressor compound: inorganic sulfate in the case of fungi and cysteine in the case of A. aerogenes. The work described in this paper indicates that there may be two independent functional corepressors of arylsulfatase synthesis in Klebsiella aerogenes W70. MATERIALS AND METHODS Bacterial strains and growth conditions. The strains employed in this work are listed in Table 1. They are derivatives of K. aerogenes W70 described by MacPhee et al. (11). Organisms were cultured as described previously (1), except that 50 1sg of L-leucine, L-cysteine, or both were added per mg when required, and cells were grown at 37 C.