Effects of bienzyme complex formation of cysteine synthetase from escherichia coli on some properties and kinetics.
Some properties and kinetics of the free and bound serine acetyltransferases (SATs) and O-acetylserine sulfhydrylase-As (OASS-As) from Escherichia coli were investigated. In some cases, SATdeltaC20, deleting 20 amino acid residues from the C-terminus of the wild-type SAT (Biosci. Biotechnol. Biochem., 63, 168-179 (1999)) was tested for comparison. The optimum pH and stability against some reagents for the free and bound wild-type SATs were similar except for the resistance to cold inactivation. The kinetics for the wild-type SAT and SATdeltaC20 followed a Ping-Pong Bi Bi mechanism with a mixed-type inhibition by L-cysteine. The kinetics and kinetic constants for the wild-type SAT were not changed by the complex formation with OASS-A. The optimum pH for OASS-A was shifted towards an alkaline pH by the complex formation. Thermal stability and stability against some reagents for the free and bound OASS-As were almost the same. On the other hand, the maximum velocity for OASS-A was lowered and dissociation constants for the substrates and products were increased by forming the complex with the wild-type SAT, although the kinetics for the free and bound enzymes followed the same Ping-Pong Bi Bi mechanism. From comparisons of computed courses of L-cysteine formation from L-serine using SAT (wild-type SAT and SATdeltaC20) and OASS-A with the experimental results and changes in the stability of the wild-type SAT by the complex formation, we discuss the role and significance of a complex formation for the cysteine synthetase.
Mino
K
K
Department of Bioscience and Biotechnology, Faculty of Engineering, Okayama University, Japan.
Yamanoue
T
T
Sakiyama
T
T
Eisaki
N
N
Matsuyama
A
A
Nakanishi
K
K
D000123:Acetyltransferases / Q000378:metabolism; D003545:Cysteine / Q000096:biosynthesis; D003547:Cysteine Synthase / Q000378:metabolism*; D004228:Dithionitrobenzoic Acid / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011487:Protein Conformation; D012694:Serine / Q000031:analogs & derivatives / Q000378:metabolism; D051050:Serine O-Acetyltransferase
D012694:Serine; D004228:Dithionitrobenzoic Acid; D000123:Acetyltransferases; D051050:Serine O-Acetyltransferase; D003547:Cysteine Synthase; D003545:Cysteine; C012162:N-acetylserine