A Novel NADP⁺-dependent Serine Dehydrogenase from Agrobacterium tumefaciens

Abstract

NADP⁺-dependent serine dehydrogenase [EC 1.1.1.–], which catalyzes the oxidation of the hydroxyl group of serine to form 2-aminomalonate semialdehyde, was purified to homogeneity from a crude extract of Agrobacterium tumefaciens ICR 1600. The enzyme had a molecular mass of about 100 kDa and consisted of four identical subunits. In addition to l-serine, d-serine, l-glycerate, d-glycerate, and 2-methyl-dl-serine were substrates. However, O-methyl-dl-serine and l-threonine were inert. The enzyme showed maximal activity at about pH 9 for the oxidation of l-serine. The enzyme required NADP⁺ as a coenzyme, NAD ⁺ was inert. The enzyme was not inhibited by EDTA, o-phenanthroline, or α, α′-dipyridyl, but was inhibited by HgCl₂, p-chloromercuribenzoate, l-cysteine, d-cysteine, malonate, 2-methylmalonate, and tartronate. The Michaelis constants for l-serine, d-serine, and NADP⁺ were 42, 44, and 0.029 mm, respectively.

Key words:

• serine dehydrogenase
• Agrobacterium tumefaciens
• oxidation of serine
• short-chain alcohol dehydrogenase