Purification of Recombinant Human 6His-FAD Synthase (Isoform 2) and Quantitation of FAD/Protein Monomer Ratio by UV-Vis Spectra

Here we describe a protocol for a one-step purification of a soluble form of human FAD synthase (isoform 2; hFADS2), overexpressed as a 6-His-tagged fusion protein in Escherichia coli, with a yield of about 15 mg from 1 L of transformed bacterial culture. Following a desalting procedure, the protein is obtained in its FAD-bound form (about 0.8 molecules of FAD per 1 protein monomer). A simple method is also proposed here, for the rapid estimation of the [FAD]/[protein monomer] ratio, starting from the typical flavoprotein spectrum of the purified protein fraction. The procedure described gives the protein at a quite high grade of purity (about 95%) and in its bifunctional (2.7.7.2/3.6.1.18) enzymatically active form, useful for further kinetical and molecular characterization.