Abstract
Abstract A two-step pathway from l-serine to l-cysteine is described in Escherichia coli and Salmonella typhimurium. Serine transacetylase, the first enzyme in this pathway, catalyzes the formation of O-acetyl-l-serine from l-serine and acetyl coenzyme A and is inhibited by l-cysteine. The enzyme has been purified approximately 1000-fold and has a spectrum similar to that of pyridoxal phosphate-containing enzymes. O-Acetylserine sulfhydrylase, the second enzyme in the pathway, catalyzes the formation of l-cysteine from O-acetyl-l-serine and sulfide. It is repressed in Salmonella grown on l-cysteine and derepressed when grown on l-djenkolic acid. Cys E mutants in S. typhimurium contain low or undetectable levels of serine transacetylase and variable levels of O-acetylserine sulfhydrylase.
Highlights
It has been established that the synthesis of cysteine in animals takes place by trans-sulfuration from homocysteine to serine, nutritional data suggest that in microorganisms a different pathway of cysteine biosynthesis de nova exists (1)
The purpose of this paper is to describe the purification and characterization of enzymic activities in E. coli and S. typhim&urn, which catalyze the conversion of L-serine to n-cysteine in two steps as follows: L-Serine + acetyl-CoA + 0-acetyl-L-serine + CoA (1)
The enzymatic, nutritional, and genetic data presented indicate that the pathway of L-cysteine biosynthesis from L-serine and sulfide in E. coli and S. typhimurium proceeds by the pathway presented in the introduction
Summary
The purpose of this paper is to describe the purification and characterization of enzymic activities in E. coli and S. typhim&urn, which catalyze the conversion of L-serine to n-cysteine in two steps as follows:
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