Influence of copper and zinc ions on toxicity of sodium N-methyldithiocarbamate to Fusarium oxysporum f. sp. lycopersici

Summary It was found that dl-lactate, acetate, pyruvate, succinate, fumarate, malate, oxalacetate and L-aspartate stimulated considerably the production of the antitumor L-asparaginase EC-2 by a colicinogenic strain of E. coli in Tryptone medium. While in the absence of these stimulative substances enzyme production was about 0.01 IU/mg dry weight, it reached 0.57–1.18 IU/mg in the presence of the substances named above. Maximum effects were obtained at the concentrations 0.025–0.1 M; at higher concentrations enzyme production decreased. L-asparagine raised the enzyme production from 0.05 IU/mg to 0.70 IU/mg; in order to obtain this effect, however, it was necessary to lower the oxygen absorption rate. Citrate and -ketoglutarate had no stimulatory effect; the effect of L-glutamate was negligible. In the cases of dl-lactate, pyruvate and L-aspartate the dependence of stimulatory effects on the time of addition of the stimulants was studied. It was found that in the case of pyruvate and especially of dl-lactate enzyme production increased rapidly between the 4 and 6 h of cultivation, i.e. at the end of the exponential growth phase; it did not matter whether the stimulant had been added at zero, 2 or 4 h of cultivation. In the case of L-aspartate the situation was principally similar, though the enzyme production started later and increased more slowly.