When exposed to hypotonic growth medium, Ehrlich
ascites carcinoma cells showed a rapid stimulation of
ornithine decarboxylase (EC 4.1.1.17) activity in 4 h, followed by a rise in their
putrescine content. This effect was totally abolished by addition of a slightly hypertonic concentration of
sodium chloride or
sucrose to the medium. The general
protein synthesis was unaffected by the hypotonic treatment. The uptake of
putrescine and, to a lesser extent,
spermidine was enhanced, the conversion of the radioactive
putrescine into
spermidine appeared partially inhibited during later stages of the hypotonic treatment. As a result, the half-life of
putrescine increased from 2.8 h under isoosmotic conditions to 7.3 h in hypoosmotic medium. Both exogenous ([14C]-
putrescine-derived) and endogenous ([14C]
ornithine-derived)
putrescine degraded at similar rates in control and hypotonic cells, yet the
putrescine taken from the medium degraded preferably to nonpolyamine products, while the
putrescine synthetized in the cell was converted evenly to
spermidine and to other metabolites. Adenosyl-
methionine decarboxylase activity (EC 4.1.1.50), which provides the second precursor for
spermidine and
spermine synthesis, was distinctly inhibited in the hypotonic medium. Inhibition was likewise observed in
spermidine synthase activity, while
spermine synthase was marginally stimulated. It appears that the hypotonic treatment serves a special condition under which not only the formation of
putrescine is enhanced dramatically but the cells also attempt to converse the
diamine by preventing its further metabolism to higher
polyamines.