Interaction of alpha 2-macroglobulin with L-asparaginase.

Abstract

Obvious protection of the catalytic activity of Esch. coli L-asparaginase by alpha 2-macroglobulin (alpha 2M) was observed under conditions otherwise propitious to the dissociation of the tetrameric molecule into inactive subunits, i.e. very diluted enzyme solutions or the presence of either SDS or urea. The degree of protection depended on enzyme and alpha 2M concentrations respectively, and on the preincubation time of the alpha 2M-enzyme mixture prior to substrate addition. The formation of a catalytically active complex between alpha 2M and L-asparaginase was confirmed by gel filtration on a Sephadex-G column and by polyacrylamide gel electrophoresis. The fact that the migration distance of the active complex corresponded to the migration of alpha 2M and the absence in that case of a migration band corresponding to the intact molecule suggest that complexing of the enzyme with alpha 2M prevented its dissociation into subunits and thus its inactivation. Addition of alpha 2M to the already dissociated enzyme molecule did not restore its catalytic activity. Alpha2-macroglobulin was shown to have an inhibiting effect on the proteolytic activity of almost all proteases and no effect on their esterolytic activity. Furthermore, it prevents the inhibition of esterolytic activity by some natural compounds. The effect of alpha 2M on other types of catalytic activity has not been investigated enough to afford a generalization of the possible role of this macroglobulin in the control of enzyme activity in the body. This paper reports the results of an in vitro study of the effect of alpha 2M on the catalytic activity of an important amidase, i.e. L-asparaginase (L-asparagine amidohydrolase 3.5.1.1), which in recent years has been used in the treatment of acute lymphocytic leukemia in children.