SUMMARY: No β-galactosidase was formed when nitrogen-depleted cells of 1433 were treated with lactose unless a source of nitrogen was added to the cells. In the presence of an exogenous nitrogen source there was an appreciable delay between the addition of lactose and the appearance of induced β-galactosidase activity. In contrast, induced increases of nitrate- and tetrathionate-reductase activities were developed without appreciable delay when depleted cells were treated with nitrate and tetrathionate, respectively, in the absence of additional nitrogen sources. The total amounts of the reductase activities developed in depleted cells were less than those obtained with non-depleted cells. The total amount of nitrate reductase activity formed was only slightly increased in the presence of ammonium sulphate, whereas normal degrees of activity were attained in the presence of casein hydrolysate. Ammonium sulphate markedly stimulated the formation of tetrathionate reductase activity.


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