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Production of polygalacturonic acid (PGA)trans -eliminase was greatly stimulated under conditions of restricted growth ofAeromonas liquefaciens . This was accomplished either by substrate restriction in a continuous-feeding culture or by restricting divalent cations in a batch culture, with the use of PGA as the sole source of carbon in a chemically defined medium containing inorganic nitrogen. Slow feeding of glucose, glycerol, or PGA to carbon-limited cultures allowed PGAtrans -eliminase to be formed at a maximum differential rate 500 times greater than in batch cultures with excess substrate present. The differential rate of enzyme formation obtained by slow feeding of these three substrances or of a mixture of PGA plus glucose was observed to be the same. Therefore, PGAtrans -eliminase produced byA. liquefaciens , contrary to the current view, appears to be constitutive. These observations also indicate that production of PGAtrans -eliminase is subject to catabolite repression and that limiting the substrate reverses this repression. It was also found that, under conditions of unrestricted growth, any compound which the bacteria can use as a source of carbon and energy repressed constitutive PGAtrans -eliminase production. The heritable reversal of catabolite repression of PGAtrans -eliminase synthesis was demonstrated by isolation of mutant strain Gc-6 which can readily synthesize the constitutive catabolic enzyme PGAtrans -eliminase while growing in the presence of excess substrate.

Production and Catabolite Repression of the Constitutive Polygalacturonic Acid trans -Eliminase of Aeromonas liquefaciens