Argininosuccinate synthetase-lyase activity in HeLa or mouse L cells increased markedly following infection by vaccinia virus. A repression mechanism determines specific activities in uninfected cells and greater activity was obtained in the presence of 0.2 m-citrulline than of 0.6 m-arginine. However, maximum activity in infected cells was obtained with 0.6 m-arginine. The development of increased enzyme activity in virus-infected cells was inhibited by puromycin or actinomycin D. Treatment of infected cells with FUdR resulted in higher levels of activity than in similar cells in the absence of the inhibitor. The Michaelis constants of enzymes in HeLa and mouse L cells were 0.11 × 10 and 0.07 × 10 , respectively; the same value of 1.0 × 10 was determined for both species of infected cells. Amino acid analysis of purified vaccinia virus prepared from HeLa cell cultures infected in the presence of [C]-carbamoyl-citrulline showed that radioactivity was associated exclusively with arginine. It is concluded that the anabolism of arginine from citrulline in vaccinia virus-infected cells is determined by virus-coded enzymes.


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