Biosynthetic Threonine Deaminase from Proteus morganii

概要

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Biosynthetic threonine deaminase was purified to an apparent homogeneous state from the cell extract of Proteus morganii, with an overall yield of 7.5%. The enzyme had a s020, w of 10.0 S, and the molecular weight was calculated to be approximately, 228, 000. The molecular weight of a subunit of the enzyme was estimated to be 58, 000 by sodium dodecyl sulfate gel electrophoresis. The enzyme seemed to have a tetrameric structure consisting of identical subunits. The enzymehad a marked yellow color with an absorption maximum at 415 nm and contained 2mol of pyridoxal 5-phosphate per mol. The threonine deaminase catalyzed the deamination of L-threonine, L-serine, L-cysteine and β-chloro-L-alanine. Km values for L-threonine and L-serine were 3.2 and 7.1mM, respectively. The enzyme was not activated by AMP, ADP and ATP, but was inhibited by L-isoleucine. The Ki for L-isoleucine was 1.17 mM, and the inhibition was not recovered by L-valine. Treatment with mercuric chloride effectively protected the enzyme from inhibition by L-isoleucine.
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