Tumor inhibitory and non-tumor inhibitory L-asparaginases from Pseudomonas geniculata.
Two enzymes that catalyze the hydrolysis of l-asparagine have been isolated from extracts of Pseudomonas 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 with l-asparagine as substrate, whereas the asparaginase AG hydrolyzes l-asparagine and l-glutamine at approximately equal rates and it is also active with d-asparagine and d-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 the K(m) values for l-asparagine for the two enzymes. The asparaginase A has a K(m) value of 1 x 10(-3) M for this substrate whereas the corresponding value for the AG enzyme is 1.5 x 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 muM.
D000818:Animals; D000942:Antigens, Bacterial; D001215:Asparaginase / Q000302:isolation & purification / Q000502:physiology / Q000627:therapeutic use*; D001216:Asparagine / Q000378:metabolism; D003429:Cross Reactions; D005973:Glutamine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008970:Molecular Weight; D009374:Neoplasms, Experimental / Q000188:drug therapy*; D011549:Pseudomonas / Q000201:enzymology*; D013379:Substrate Specificity
D000942:Antigens, Bacterial; D005973:Glutamine; D001216:Asparagine; D001215:Asparaginase