Cysteine and S-sulphocysteine biosynthesis in bacteria

Summary Four components of O-acetylserine (OAS) sulphhydrylase with different molecular weights have been detected in extracts of Pseudomonas aeruginosa. This bacterium also contained an enzyme, S-sulphocysteine synthase, which catalysed the formation of S-sulphocysteine from OAS and thiosulphate. The latter enzyme was possibly associated with a low molecular weight form of OAS sulphhydrylase. Some properties of OAS sulphhydrylase and S-sulphocysteine synthase in P. aeruginosa are reported.The distribution of OAS sulphhydrylase, serine transacetylase and S-sulphocysteine synthase in a number of bacteria including sulphur photoautotrophs, sulphur chemoautotrophs and dissimilatory sulphate reducers was examined.All organisms contained the first two enzymes but only about half had S-sulphocysteine synthase. There was no correlation between the presence of S-sulphocysteine synthase and other aspects of sulphur metabolism in the organisms studied or the source of sulphur in the growth medium. No enzymic degradation of S-sulphocysteine was detected in P. aeruginosa. Strong repression of OAS sulphhydrylase synthesis by cysteine occurred in Escherichia coli and Rhodopseudomonas spheroides but in P. aeruginosa, Bacillus megaterium and Desulfotomaculum nigrificans the levels of the enzyme did not correlate with the source of sulphur for growth.