SQOR and periodontitis: Landry et al. noted inner-mitochondrial-membrane lipids can amplify sulfite interference; in periodontitis, methanethiol (MeSH) generates non-metabolizable methyl-polysulfide (MeSSH) that blocks the SQOR pathway; Romanelli-Cedrezz et al. showed in C. elegans that SQRD-1 uses UQ or RQ to detoxify H2S, whereas SQRD-2 acts as a negative regulator