Abstract A gene encoding an l-lysine dehydrogenase was identified in the hyperthermophilic archaeon Pyrococcus horikoshii. The gene was overexpressed in Escherichia coli, and its product was purified and characterized. The expressed enzyme is the most thermostable l- lysine dehydrogenase yet described, with a half-life of 180 min at 100 C. The product of the enzyme's catalytic activity is Δ 1-piperideine-6-carboxylate, which makes this enzyme an l- ...