Kinetic Analysis of Iron-Dependent Histone Demethylases: α-Ketoglutarate Substrate Inhibition and Potential Relevance to the Regulation of Histone Demethylation in Cancer Cells

The Jumonji C domain-containing histone demethylases (JmjC-HDMs) are alpha-ketoglutarate (alpha KG)-dependent, O-2-activating, non-heme iron enzymes that play an important role in epigenetics. Reported herein is a detailed kinetic analysis of three JmjC-HDMs, including the cancer-relevant JMJD2C, that was achieved by employing three enzyme activity assays. A continuous 02 consumption assay reveals that HDMs have low affinities for O-2, suggesting that these enzymes can act as oxygen sensors in vivo. An interesting case of alpha KG substrate inhibition was found, and the kinetic data suggest that alpha KG inhibits JMJD2C competitively with respect to O-2 center dot JMJD2C displays an optimal activity in vitro at alpha KG concentrations similar to those found in cancer cells, with implications for the regulation of histone demethylation activity in cancer versus normal cells.