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

AUTOR(ES)
RESUMO

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 Km values for l-asparagine for the two enzymes. The asparaginase A has a Km 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.

ACESSO AO ARTIGO

Documentos Relacionados