Homologous and heterologous interactions between catalytic and regulatory subunits of Escherichia coli acetohydroxyacid synthase I and III

Homologous and heterologous interactions between acetohydroxyacid synthase (AHAS) I and III from E. coli have been studied by surface plasmon resonance (SPR). The catalytic and regulatory subunits association for AHAS I (K (D) = 1.13 x 10(-7) M) was stronger than that for AHAS III (K (D) = 5.29 x 10(-7) M). A strong heterologous association between regulatory and catalytic subunits and heterologous activation of catalytic subunits were observed. SPR results combined with enzyme kinetics indicate that the reconstituted heterologous enzymes had similar kinetic properties as homologous enzymes, implying that the regulatory subunit of AHAS I could be replaced by the regulatory subunit of AHAS III and vice versa. This work may be useful to further understandings of the mechanism of regulation of AHAS.