245: Zhu et al. (2005) The Selective Cause of an Ancient Adaptation. Science 307 (5713): 1279

Science -- Zhu et al. 307 (5713): 1279:

Phylogenetic analysis reveals that the use of nicotinamide adenine dinucleotide phosphate (NADP) by prokaryotic isocitrate dehydrogenase (IDH) arose around the time eukaryotic mitochondria first appeared, about 3.5 billion years ago.

Then they did an experiment showing how the evolution of NADP use occurred.