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Two enzymes that catalyze the hydrolysis ofl -asparagine have been isolated from extracts ofPseudomonas geniculata . After initial salt fractionation, the enzymes were separated by chromatography on diethylaminoethyl-Sephadex and purified to homogeneity by gel filtration, ion-exchange chromatography, and preparative polyacrylamide electrophoresis. The enzymes differ markedly in physicochemical properties. One enzyme, termed asparaginase A, has a molecular weight of approximately 96,000 whereas the other, termed asparaginase AG, has a molecular weight of approximately 135,000. Both enzymes are tetrameric. The asparaginase A shows activity only withl -asparagine as substrate, whereas the asparaginase AG hydrolyzesl -asparagine andl -glutamine at approximately equal rates and it is also active withd -asparagine andd -glutamine as substrates. The asparaginase A was found to be devoid of antitumor activity in mice, whereas the asparaginase AG was effective in increasing the mean survival times of both C3H mice carrying the asparagine-requiring Gardner 6C3HED tumor line and Swiss mice bearing the glutamine-requiring Ehrlich ascites tumor line. These differences in antitumor activity were related to differences in theKm values forl -asparagine for the two enzymes. The asparaginase A has aKm value of 1 × 10−3 M for this substrate whereas the corresponding value for the AG enzyme is 1.5 × 10−5 M. Thus the concentration of asparagine necessary for maximal activity of the asparaginase A is very high compared with that of the normal plasma level of asparagine, which is approximately 50 μM.

Tumor Inhibitory and Non-Tumor Inhibitory l -Asparaginases from Pseudomonas geniculata