Recently, a new set of transcriptional regulators has been discovered from the aerobic, polychlorinated biphenyl (PCB) degrading bacterium Burkholderia xenovorans, an organism which was originally found living in landfill sites in upstate New York. These proteins are designated as “regulators of CO metabolism” (RcoM) because they are able to sense CO in order to allow Burkholderia xenovorans to use CO as an energy source. Much like CooA, RcoM utilizes heme in order to sense the presence of CO. The binding of CO to the Fe(II) heme of RcoM functions by causing the protein’s LytTR domain to bind DNA and turn on transcription, initiating the creation of biological machinery needed to metabolize CO. Although RcoM utilizes heme in a manner similar to CooA, it comes from a different protein structural family. To date, no structure of RcoM has been solved. Therefore, we are utilizing covelent modification mass spectrometry to try to elucidate structural information and compare the structure-function relationships of RcoM and CooA.