In addition to methionine, aspartate may also induce sporulation in the Streptomyces fradiae St3110 mutant that requires methionine for sporulation but not for growth. Partially purified aspartokinase (EC 2.7.2.4.) of the mutant was tested for feed-back control by methionine, threonine, and lysine. Methionine or threonine alone did not have any significant effect but they had a concerted inhibitory effect together that was further increased by lysine. The threonine-lysine combination also caused inhibition of the enzyme activity, while lysine alone activated the enzyme. Methionine was also found to partially repress the aspartokinase activity to about one third of the control. The sporulating aerial mycelia induced by aspartate were lacking the characteristic sporulation pigmentation present in the wild type or after induction of spores by methionine. No significant difference in heat resistance between the two types of the spores was detected. The number of spores produced by aspartate was only about one fourth of that after induction by methionine. The data may indicate a role of aspartokinase control by methionine in restoring the normal sporulation, although in addition to this methionine may act by a different mechanism, as well.
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