Increase in the Stability of Serine Acetyltransferase from Escherichia coli against Cold Inactivation and Proteolysis by Forming a Bienzyme Complex

概要

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Cysteine synthetase from Escherichia coli is a bienzyme complex composed of serine acetyltransferase(SAT) and O-acetylserine sulfhydrylase-A (OASS). The effects of the complex formation on the stability of SAT against cold inactivation and proteolysis were investi gated. SAT was reversibly inactivated on cooling to 0℃. Ultracentrifugal analysis showed that SAT (a hexamer) was dissociated mostly into two timers on cooling to 0℃ in the absence of OASS, while in the presence of GASS one trimer of the SAT subunits formed a complex with one dimer of OASS subunits. In the presence of GASS, not only the cold inactivation rate was reduced but also the reactivation rate was increased. Furthermore, SAT became stable against proteolytic attack by a-chymotrypsin and V8 protease by forming the complex with OASS. On the other hand, SAT was degraded by trypsin in the same manner both in the presence and in the absence of OASS. The different tendency in the stability against proteolysis with the different proteases was discussed with respect to the substrate specificity of the proteases and amino acid sequence of the C-terminal region of SAT that interacts with OASS.
社団法人日本農芸化学会の論文
2001-04-23