Novel thiols of prokaryotes

Glutathione metabolism is associated with oxygenic cyanobacteria and the ox ygen-utilizing purple bacteria, but is absent in many other prokaryotes. Th is review focuses on novel thiols found in those bacteria lacking glutathio ne. Included are glutathione amide and its perthiol, produced by phototroph ic purple sulfur bacteria and apparently involved in their sulfide metaboli sm. Among archaebacteria, coenzyme M, (2-mercaptoethanesulfonic acid) and c oenzyme B (7-mercaptoheptanoylthreonine phosphate) play central roles in th e anaerobic production of CH4 and associated energy conversion by methanoge ns, whereas the major thiol in the aerobic phototrophic halobacteria is gam ma -glutamylcysteine. The highly aerobic actinomycetes produce mycothiol, a conjugate of N-acetylcysteine with a pseudodisaccharide of glucosamine and myo-inositol, AcCys-GIcN alpha (1 --> 1)Ins, which appears to play an anti oxidant role similar to glutathione. Ergothioneine, also produced by actino mycetes, remains a mystery despite many years of study. Available data on t he biosynthesis and metabolism of these and other novel thiols is summarize d and key areas for additional study are identified.