Catalyzes the NADPH-dependent reductive condensation of pyruvate to the intermediate formed by the adjacently encoded enzyme y2836, namely (2S)-2-amino-4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}butanoate, leading to the production of yersinopine. This is the last step in the biosynthesis of the metallophore yersinopine, which is involved in metal acquisition and thus enables bacterial growth inside the host, where metal access is limited. Therefore, this enzyme probably contributes to Yersinia virulence. Cannot use alpha-ketoglutarate in place of pyruvate, and displays only poor efficiency with oxaloacetate and glyoxylate. H2O + NADP(+) + yersinopine = (2S)-2-amino-4-{[(1S)-1-carboxy-2-(1H-imidazol-4-yl)ethyl]amino}butanoate + H(+) + NADPH + pyruvate kcat is 0.30 sec(-1) with pyruvate as substrate. kcat is 0.29 sec(-1) with oxaloacetate as substrate. kcat is 0.22 sec(-1) with glyoxylate as substrate (at pH 8.0 and 22 degrees Celsius). Homodimer. Belongs to the staphylopine dehydrogenase family. Extended N-terminus. Extended N-terminus.