Kinetic Study of Thermostable L-Threonine Dehydrogenase from an Archaeon Pyrococcus horikoshii (Enzymology, Protein Engineering, and Enzyme Technology)

概要

論文の詳細を見る
In the genome data base of the hyperthermophilic archaeon Pyrococcus horikoshii, an open reading frame with sequence homology to a gene encoding alcohol dehydrogenase was found. It was demonstrated that the encoded enzyme was a thermostable L-threonine dehydrogenase which can oxidize the hydroxy alkyl residue of L-threonine associated with the reduction of NAD^+ or NADP^+. This enzyme is a member of the zinc-containing L-threonine dehydrogenase family. One enzyme molecule contained one zinc atom, and this metal was considered to contribute to the hyperthermostablility of the enzyme. The reaction of the enzyme proceeded via a sequential mechanism. The Michaelis constants (K_m) for L-threonine and NAD^+ were 0.013 and 0.010 mM, respectively, and the maximum reaction rate (V_<max>) was 1.75 mmol NADH formed/min/mg-protein at 65℃. The K_m values for both L-threonine and NADP^+ were larger than those for L-threonine and NAD^+ with a similar V_<max> value. These results indicate that the enzyme has lower affinity to NADP^+ than to NAD^+, and the binding affinity for L-threonine depends on the coenzymes.
社団法人日本生物工学会の論文
2005-02-25