Substrate specificity of overexpressed and purified ketoisovalerate reductase KivRFp. 5A). Specific activity of reductive reaction of different homologous compounds using NADPH (0.29 mM) as coenzyme. 2-ketoisovalerate (2-Kiv), 2-ketovalerate (2-Kva), pyruvate, 2-ketocapronate (2-Kca), 2-ketoglutarate (2-Kgl), and 2-ketobutyrate (2-Kbu). 5B). Specific activity of reductive reaction of different coenzymes using 2-Kiv (0.7 mM) as substrate. Relative activity was shown as the percentage of the activity of the activity towards 2-ketoisovalerate. All measurements were performed in triplicate.