Refolding of porcine growth hormone from inclusion bodies of Escherichia coli

Escherichia coli cells expressing porcine growth hormone were grown in a batch fermentation process. The expression level was estimated to be nearly 40% of the total cellular protein after 2-3 h of induction with 1 mM isopropyl beta-D-thiogalactoside. Porcine growth hormone expressed as inclusion bodies was solubilized in 8 M urea. Refolding conditions following a dilution protocol in the presence of beta-mercaptoethanol or using a glutathione pair were tested. Reverse phase-HPLC was applied to distinguish oxidized, misfolded and reduced forms of the hormone. A ratio of reduced to oxidized glutathione equal to 2/1 was chosen to avoid the formation of misfolded forms at high protein concentration.