Escherichia coli B synthesized ß-galactosidase and an enzyme system for D-xylose when exposed to lactose and xylose respectively in nitrogen-free media. The amount of ß-galactosidase formed in the absence of external nitrogen depended upon the nature of the medium in which the cells had originally been grown. Half as much of this enzyme was synthesized without exogenous nitrogen by cells taken from a nitrogen-rich medium as was formed by cells under favorable conditions with an external supply of nitrogen. Escherichia coli B contained a pool of nitrogen compounds soluble in 80 per cent ethanol and made up of several ninhydrin-positive components. One of these was identified chromatographically as glycine using an authentic radioactive sample. Another substance behaved like serine on the chromatograms. The internal pool of amino acids and peptides was large enough to account for the ß-galactosidase synthesized by cells exposed to lactose in a medium free of nitrogen. Some degree of interaction of the syntheses of the ß-galactosidase and xylose enzyme systems was observed in nitrogen-free media. This interaction produced a greater effect on the formation of ß-galactosidase and was attributed to a limiting factor(s) in the internal nitrogenous pool or to a limiting intermediate in enzyme synthesis.

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