To determine if the recombinant enzymes were functional, both GST fusion proteins were used in an enzymatic assay. The presence of GlcNAc and the formation of the intermediate product ManNAc and the final product NeuNAc were monitored using HPLC-MS analysis and results are presented in Figure 3 . Application of the GST-fusion proteins of both enzymes in the in vitro assay led to the formation of ManNAc and NeuNAc demonstrating that the synthetic genes are expressed as functional proteins (Figure 3a1 and 3b1) .