A new assay for L-asparagine synthetase.

A fast, relatively inexpensive method of measuring the enzymatic formation of L-asparagine from L-aspartate is presented. This radiochemical assay requires simple manipulations making it ideal for working with large numbers of samples, while maintaining high sensitivity and reproducibility. A mechanism similar to the enzymatic beta-decarboxylation of aspartate is utilized but in a nonenzymatic reaction. In the presence of pyridoxal and A13+ ions, the 14C of L-[4-14C]aspartate is decarboxylated while L-[4-14C]asparagine remains intact. This assay is shown to be suitable for measuring mammalian L-asparagine synthetase activity, while not requiring the isolation of assay enzymes.