Inhibitory effect of L-asparaginase in lymphocyte transformation induced by phytohemagglutinin.

The effect of Escherichia coli L-asparaginase on phytohemagglutinin (PHA)-induced transformation of human lymphocytes was studied. Transformation was remarkably suppressed by the enzyme when it was added to the cul ture not later than 24 hr after its initiation. The effective concentration was more than 0.2 i.u./tube. Guinea pig serum and L-0-aspartohydroxamic acid, an L-asparagine analog, have a suppressive effect on lymphocyte transfor mation in this system. PHA-treated lymphocytes became sensitive to L-asparaginase 12 hr after the culture was started, while no L-asparagine dependency was detected at any stage of the culture. An addition of L-asparagine or L-glutamine to the culture system treated with both PHA and L-asparaginase at zero time caused the partial re covery of thymidine-'H uptake.