Inhibition Assay: Hydroxylated HIF bonds specifically to the von Hippel-Lindau protein-elongin B-elongin C complex (VBC complex). This interaction occurs only if HIF is hydroxylated on a conserved prolyl radical. It is the basis for the biochemical determination of HIF prolyl hydroxylase activity. The test is carried out as described [Oehme F., Jonghaus W., Narouz-Ott L., Huetter J., Flamme I., Anal. Biochem. 330 (1), 74-80 (2004)]:A clear 96-well microtiter plate coated with NeutrAvidin HBC (Pierce) is incubated with blocker casein for 30 minutes. The plate is then washed three times with 200 ul each time of wash buffer (50 mM Tris, pH 7.5, 100 mM NaCl, 10% (v/v) blocker casein, 0.05% (v/v) Tween 20) per well. The peptide biotin-DLDLEMLAPYIPMDDDFQL (Eurogentec, 4102 Seraing, Belgium) is added in a concentration of 400 nM in 100 ul wash buffer. This peptide serves as a substrate for the prolyl hydroxylation and is bonded to the microtiter plate.