Biodegradative threonine deaminase from Proteus morganii.

Abstract

Biodegradative threonine deaminase was purified and crystallized from cells of Proteus morganii grown aerobically in the medium containing high concentrations of amino acids. The enzyme was homogeneous by the criteria of ultracentrifugation and SDS disc gel electrophoresis. The molecular weight of the enzyme was determined to be approximately 120, 000 by the gel filtration method. The molecular weight of subunit of the enzyme was estimated to be 32, 000 by SDS disc gel electrophoresis. The enzyme seems to have a tetrameric structure consisting of identical subunits. The enzyme has a marked yellow color with an absorption maximum at 415 nm and contains 4 moles of pyridoxal phosphate per mole of enzyme protein. The threonine deaminase was activated by AMP and ADP. It catalyzed the deamination of L-threonine, L-serine and β-chloro-L-alanine. The optimal pH was about 9.0 in the absence of AMP. In the presence of 1mM AMP, the optimal pH became in a range between 8.0 and 9.5. The enzyme was not inhibited by L-isoleucine. Its Km values for L-threonine were found to be 1.5mM and 24mM, in the presence and absence of 1mM AMP, respectively. The Ka value for AMP was found to be 0.55mM at the threonine concentration of 5mM. However, the value was varied depending on the concentration of L-threonine.