Inhibition of homoserine dehydrogenase I by L-serine in Escherichia coli.
We have reported that a major cause of growth inhibition of Escherichia coli by L-serine is its inhibition of homoserine dehydrogenase I (HDH I), which is involved in the biosyntheses of threonine and isoleucine [Hama, H., Sumita, Y., Kakutani, Y., Tsuda, M., & Tsuchiya, T. (1990) Biochem. Biophys. Res. Commun. 168, 1211-1216]. However, Patte et al. reported that L-serine does not inhibit HDH I [Patte, J.-C., Truffa-Bachi, P., & Cohen, G.N. (1966) Biochim. Biophys. Acta 128, 426-439]. In studies on the reason for these discrepant results, we found that the concentration of K+ and the pH in the assay mixture strongly influenced the inhibitory effect of L-serine. L-Serine strongly inhibited the HDH I activities in both the forward and reverse reactions between aspartate semialdehyde and homoserine at a physiological K+ concentration (100 to 200 mM) and physiological pH (7.5) for E. coli cells. On the other hand, two well-known inhibitors of HDH I, L-threonine and L-cysteine, strongly inhibited the activity regardless of the K+ concentration and pH.
Hama
H
H
Department of Microbiology, Faculty of Pharmaceutical Sciences, Okayama University.
Kayahara
T
T
Tsuda
M
M
Tsuchiya
T
T
D002414:Cations, Monovalent; D003545:Cysteine / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D006715:Homoserine Dehydrogenase / Q000037:antagonists & inhibitors*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011188:Potassium / Q000494:pharmacology; D012694:Serine / Q000494:pharmacology*; D013912:Threonine / Q000494:pharmacology
D002414:Cations, Monovalent; D013912:Threonine; D012694:Serine; D006715:Homoserine Dehydrogenase; D003545:Cysteine; D011188:Potassium