3-Hydroxyisobutyrate Dehydrogenase fromPseudomonas putidaE23: Purification and Characterization

Abstract
The NAD+-dependent 3-hydroxyisobutyrate dehydrogenase [EC 1.1.1.31] was purified to homogeneity from Pseudomonas putida E23. The enzyme was a tetramer (molecular mass, 120kDa) consisted of identical subunits (molecular mass, 30 kDa). The enzyme was specific for NAD+ (Km, 0.44 mm). The maximal activity was obtained at about pH 10. The enzyme was specific for the l-isomer of 3-hydroxyisobutyrate. In addition to l-3-hydroxyisobutyrate, l-serine, 2-methyl-dl-serine, and 3-hydroxypropionate were substrates. The Km for l-3-hydroxyisobutyrate, l-serine, 2-methyl-dl-serine, and 3-hydroxypropionate were 0.12, 18, 44, and 83 mm, respectively. The enzyme was inhibited by p-chloromercuribenzoate, HgCl2, and AgNO3, but not by EDTA, α,α′-dipyridyl, and o-phenanthroline. The N-terminal 26 amino acid sequence was compared with the sequences deduced from the enzyme genes of rat liver and Pseudomonas aeruginosa.

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