Chemical modifications of Escherichia coli L-asparaginase and their effect on plasma clearance rate and other properties.

Escherichia coli asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) has been modified by succinylation, acetylation and the attachment of N,N-dimethyl-1,3-propanediamine and glucuronic acid. The effect of these modifications on plasma clearance rates in mice and on other properties is compared to the effects of modification with lactose and N-acetylneuraminyl lactose studied previously. The t 1/2 values for the acylated enzyme samples (lower pI) were reduced, succinylated asparaginase sharply and the acetylated enzyme less so. The N,N-dimethyl-1,3-propanediamine-modified samples (increased pI) also had lower t 1/2 values, but samples modified with glucuronic acid (reduced pI) showed little change in clearance time. The main conclusion is that the increased t 1/2 value found in the previous work for N-acetylneuraminyl-lactosylated enzyme is not due to the decreased pI value of the modified enzyme, but must be attributed to interference by N-acetylneuraminyl-lactose residues, directly or indirectly, with the mechanism normally used by the mouse to clear itself of injected E. coli asparaginase.