Abstract

Previously, medium containing a combination of L-serine, glycine and L-leucine (SGL medium) has been used to study the characteristics, including the activation system, of L-serine deaminase (L-SD), an interesting enzyme from Escherichia coli that is first synthesized in an inactive form. In this thesis, I isolated two new E. coli SGL- mutants through $\lambda$placMu insertion. All these mutants MEW20b and MEWb1 are quite likely involved in the activation of L-SD enzyme. Applying inverse PCR technique, I identified the mutated gene in these two mutant strains to be nuoM and torA respectively. A formerly isolated SGL- mutant MEW84 was also identified as a $\lambda$placMu insertion in the glpC gene. Further experiments proved that mutations in these three genes actually were responsible for the SGL- phenotype of the mutant strains. A comparison of the functions of the three mutated genes suggests that electron donation may be part of the process necessary to activate L-SD. Physiological studies were carried out to investigate further these three mutants.