Purification of SELP-1020-A by A) affinity chromatography and B) molecular weight determination by mass spectrometry. A) SDS-PAGE of SELP-1020-A: lane 1 – soluble lysate before column loading; lane 2 – flow through; lane 3 – fraction eluted with 20 mM imidazole; lane 4 – fraction eluted with 40 mM imidazole; lane 5 – fraction eluted with 80 mM imidazole. Fully purified polymer fraction was obtained by elution with buffer containing 80 mM of imidazole with high recovery rate. B) Image represents the MALDI-TOF mass spectrum of SELP-1020-A. The molecular ion peak at 54125 confirms the theoretical calculated value (54117 Da).