Putrescine and spermidine sensitivity of lysine decarboxylase in Escherichia coli: evidence for a constitutive enzyme and its mode of regulation.

Cells of Escherichia coli grown under physiological (noninducing) conditions have a low level of lysine decarboxylase activity. This activity differs from the enzyme found in induced cells in its sensitivity to putrescine (33% of control in the presence of 20 mM putrescine). It is also sensitive to spermidine (20% of control in the presence of 6 mM spermidine). A mixture of putrescine and spermidine completely eliminated lysine decarboxylase activity. This provides evidence for the existence of a biosynthetic enzyme and suggests a mechanism to explain the appearance of cadaverine in polyamine-depleted cells.