Transcription factor HIF-1 is a key regulator in cellular adaptation to hypoxia. HIF prolyl hydroxylases (PHDs) control HIF-1 accumulation by hydroxylation dependent on molecular oxygen. Due to this regulation, PHDs have been pointed out as potential drug targets. We have purified catalytically active human PHD3, after heterologous expression in Escherichia coli. Histidine-tagged enzyme was isolated as monomer by immobilized Ni-affinity chromatography followed by gel filtration. Overexpression of bacterial chaperonins GroEL/ES at 30 degrees C substantially increased the yield of soluble PHD3. High concentrations of salt and reducing agent during purification prevented protein aggregation. The enzyme activity with peptide derived from HIF-1 alpha was inhibited by Zn2+, desferrioxamine and imidazole. The hydroxylation activity was verified by-mass spectrometry, and Pro567 in HIF-1 alpha was discovered as a new site of hydroxylation. (c) 2007 Elsevier Inc. All rights reserved.