Hypoxia-induced gene expression is initiated when the hypoxia-inducible factor-1 (HIF-1) alpha subunit is stabilized in response to a lack of oxygen. An HIF-1alpha-specific prolyl-hydroxylase (PHD) catalyzes hydroxylation of the proline-564 and/or -402 residues of HIF-1alpha by an oxygen molecule. The hydroxyproline then interacts with the ubiquitin E3 ligase von Hippel Lindau protein and is degraded by an ubiquitin-dependent proteasome. PHD2 is the most active of three PHD isoforms in hydroxylating HIF-1alpha. Structural analysis showed that the N-terminal region of PHD2 contains a Myeloid translocation protein 8, Nervy, and DEAF1 (MYND)-type zinc finger domain, whereas the catalytic domain is located in its C-terminal region. We found that deletion of the MYND domain increased the activity of both recombinant PHD2 protein and in vitro-translated PHD2. The zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine augmented the activity of wild-type PHD2-F but not that of PHD2 lacking the MYND domain, confirming that the zinc finger domain is inhibitory. Overexpression of PHD2 lacking the MYND domain caused a greater reduction in the stability and function of HIF-1alpha than did overexpression of wild-type PHD2, indicating that the MYND domain also inhibits the catalytic activity of PHD2 in vivo.