Characteristics of serine acetyltransferase from Escherichia coli deleting different lengths of amino acid residues from the C-terminus

Some properties of serine acetyltransferases (SATs) from Escherichia coli, deleting 10-25 amino acid residues from the C-terminus (SATdeltaC10-deltaC25) were investigated. The specific activity depended only slightly on the length of the C-terminal region deleted. Although the sensitivity of SATdeltaC10 to inhibition by L-cysteine was similar to that for the wild-type SAT, it became less with further increases in the length of the amino acid residues deleted. SATdeltaC10 was inactivated on cooling to 0 degrees C and dissociated into dimers or trimers in the same manner as the wild-type SAT, but Met-256-le mutant SAT as well as SATdeltaC14, SATdeltaC20, and SATdeltaC25 were stable. Since SATdeltaC10, SATdeltaC14, and SATdeltaC25 did not form a complex with O-acetylserine sulfhydrylase-A (OASS-A) in a way similar to SATdeltaC20, it was indicated that 10 amino acid residues or fewer from the C-terminus of the wild-type SAT are responsible for the complex formation with OASS-A. The C-terminal peptide of the 10 amino acid residues interacted competitively with OASS-A with respect to OAS although its affinity was much lower than that for the wild-type SAT.