Threonine dehydratases in different strains of Streptomyces fradiae

Among Streptomyces fradiae parent strain (NRRL 2702), aspartate auxotroph strain (SMF 305), and revertant strain (SMF 306), the revertant strain is the highest producer of tylosin and showed different repression patterns of tylosin production by ammonium ion from the parent strain. These results were elucidated by the facts that the revertant strain was superior to the parent or auxotroph strain in the biosynthesis of glutamine synthetase involved in ammonium assimilation and in the biosynthesis of threonine dehydratase (TDT) involved in providing precursors necessary for tylosin production, and ammonium ion inhibited the activity of TDT purified from the parent strain more than that of TDT from the revertant strain. TDT from the parent strain has been purified by DEAE cellulose, hydroxyapatite, Mono Q HR 5/5, and reversed-phase Protein C4 chromatography. The molecular mass was 60 kDa by SDS-PAGE and 240 kDa by gel filtration. The N-terminal amino acid sequence of TDT was NH3-E-A-T-G-P-L-T-T-E-S-G-A-P-V. The activity of TDT was allosterically activated by adenosine monophosphate.