A mutant of Escherichia coli is described which is defective in the conversion of arginine to putrescine. The activity of the enzyme agmatine ureohydrolase is greatly reduced, whereas the activity of the other two enzymes of the pathway, the constitutive arginine decarboxylase and the inducible arginine decarboxylase, are within the normal range. The growth behavior of the mutant reflects the enzymatic block. It grows well in the absence of arginine, but only poorly in the presence of arginine. Under the former conditions, putrescine can be formed from ornithine as well as arginine, whereas under the latter conditions, because of feedback control, it can be formed only from arginine.

Escherichia coli K-12 possesses two active transport systems for arginine, two for ornithine, and two for lysine. In each case there is a lowand a high-affinity transport system. They have been characterized kinetically and by response to competitive inhibition by arginine, lysine, ornithine and other structurally related amino acids. Competitors inhibit the high-affinity systems of the three amino acids, whereas the low-affinity systems are not inhibited. On the basis of kinetic evidence and competition studies, it is concluded that there is a common high-affinity transport system for arginine, ornithine, and lysine, and three low-affinity specific ones. Repression studies have shown that arginine and ornithine repress each other's specific transport systems in addition to the repression of their own specific systems, whereas lysine represses its own specific transport system. The common transport system was found to be repressible only by lysine. A mutant was studied in which the uptake of arginine, ornithine, and lysine is reduced. The mutation was found to affect both the common and the specific transport systems.

The process of induction of tryptophan oxygenase in Pseudomonas acidovorans is typical of many microbial enzyme induction systems, in that it (i) requires cell multiplication and de novo protein synthesis, (ii) is subject to catabolite repression, (iii) results in the formation of a stable enzyme, whose level, upon removal of inducer, is diluted out by cell proliferation, and (iv) exhibits product induction. L-Kynurenine was more effective than L-tryptophan as an inducer of both tryptophan oxygenase and the second enzyme of the pathway, kynurenine formamidase. The occurrence of product induction of these two enzymes by their common metabolite eliminated the possibility of sequential induction of these enzymes. DL-5-Fluorotryptophan, nonmetabolizable and devoid of any inducing activity, resulted in a concentration-dependent inhibition of the L-tryptophan-mediated induction of tryptophan oxygenase; kynurenine formamidase induction, however, was not influenced by the presence of DL-5-fluorotryptophan. DL-7-Azatryptophan, also nonmetabolizable and completely inactive as an inducer, acted synergistically with L-tryptophan and superinduced tryptophan oxygenase levels. When induction was conducted in a medium containing only L-tryptophan and 7-azatryptophan as inducing agents, then tryptophan oxygenase induction was enhanced, whereas the kynurenine formamidase level was essentially unchanged. These data indicate that various inducing conditions affect the relative proportions of tryptophan oxygenase and kynurenine formamidase, and thus indicate noncoordinate regulation of these enzyme activities.

The uptake system for 6-diazo-5-oxo-L-norleucine (DON) was studied in mouse P388 leukemia cells. The DON transport system was found to resemble that of another glutamine antimetabolite, Acivicin, in its strong temperature dependence, utilization of the "L" transport system, inhibition by glutamine but not by glutamate, potent inhibition by p-chloromercuribenzene sulfonate, Na+, and only minimal inhibition by various energy poisons. A Km of approximately 70 microM and a Vmax of 3.4 nmoles/10(6) cells/min was calculated for this cell line. The accumulated DON was not metabolized by P388 cells and moderate efflux occurred at 37 degrees C. The DON transport characteristics of a DON-resistant P388 cell line (100 times ID50 of parent line) were similar to those of the DON-sensitive parent line, indicating that altered drug transport may not be involved in development of resistance to this antimetabolite. The finding that an Acivicin-resistant subline of P388 cells which exhibited good transport of DON showed negligible transport of Acivicin suggests different modes of resistance towards the two glutamine antimetabolites.

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