(A) Total cellular ATP in fibroblasts, hESCs, and iPSCs was quantified with a bioluminescence luciferase-based assay. All iPSC lines showed a similar hESC-like reduction of ATP level compared to the parental fibroblasts. Error bars indicate standard deviation (B) Bioenergetic profiling was performed using Seahorse XF96 analyzer. A reduction of the ratio between oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in hESCs and iPSCs indicated a parallel shift from respirative to fermentative metabolism in all pluripotent stem cells compared to fibroblasts. By monitoring the OCR values upon metabolic perturbations with subsequent introduction of three mitochondrial inhibitors (oligomycin, FCCP, and rotenone), we derived estimates of the following parameters of mitochondrial bioenergetics: ATP turnover, maximal respiration capacity, mitochondrial leak, non-mitochondrial oxygen consumption, and ATP reserve. All parameters, except ATP reserve were similar in all hESCs and iPSCs and distinct from fibroblasts.