The inhibition in vivo of l-asparagine synthetase (l-glutamine hydrolyzing. EC 18.104.22.168) from l-asparaginase-resistant leukemia 5178Y (L5178Y/AR) and from mouse pancreas by the ketoamino acids DON (l-DON; 6-diazo-5-oxo-l-norleucine), CONV (l-CONV; 2-amino-5-chlorolevulinic acid; 5-chloro-4-oxo-l-norvaline) and DONV (l-DONV; 5-diazo-4-oxo-l-norvaline) was investigated using both l-glutamine and ammonium chloride as substrates. In the L5178Y/AR system, DON was shown to inhibit the utilization of l-glutamine by l-asparagine synthetase in vivo to a degree comparable to that previously observed in vitro. CONV, however, was less effective in vivo than in vitro and DONV exerted no demonstrable inhibitory effect in the intact organism. In the case of the analogous enzyme from mouse pancreas, both DON and CONV effectively inhibited the utilization of l-glutamine in vivo. DONV was relatively inert in this experimental setting. The pattern of inhibition of l-asparagine synthetase was generally mirrored by the effects of these ketoamino acids on the organ pool-sizes of l-asparagine. However, CONV, alone of the three, demonstrated inhibition of the incorporation of l-asparagine into tumoral and pancreatic protein in vivo. Both DON and CONV inhibited the incorporation of [14C]formate into nucleic acid purines; this effect, in turn, most likely reflected the strong inhibition by these agents of several of the amidotransferases concerned with purine biosynthesis.
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