| This work was undertaken to further elucidate physiological requirements for glutathione (GSH)-dependent formaldehyde oxidation in Rhodobacter sphaeroides. During the course of these investigations I have provided evidence for the importance of GSH metabolism in formaldehyde oxidation through analysis of mutant strains lacking pyridine nucleotide transhydrogenase, a major source of NADPH, which is used for GSH reduction. This work also provides new evidence for the physiological role of transhydrogenase in aerobically growing cells, namely NADPH production. I have also described the presence of multiple two-component regulatory systems involved in regulating expression of a GSH-dependent formaldehyde dehydrogenase structural gene ( adhI). One of these, AfdRS (a&barbelow;ctivator of f&barbelow;ormaldehyde d&barbelow;ehydrogenase) activates expression of adhI, possibly in response to the presence of formaldehyde or its GSH adduct, S-hydroxymethyl-glutathione (HMGSH). The other, RfdRS (r&barbelow;egulator of f&barbelow;ormaldehyde d&barbelow;ehydrogenase), negatively regulates adhI expression in response to an unknown signal. Together AfdRS and RfdRS represent a strategy for regulation of GSH-FDH expression, where both positive and negative regulators are involved in controlling expression of this gene. Finally, an analysis of the completed genome sequence of R. sphaeroides has identified several genes whose products may play an important role in GSH-dependent formaldehyde oxidation in this organism, and provides multiple avenues of future research to further elucidate the physiological requirements of GSH-dependent formaldehyde metabolism. |
