Fig. 4.

Sources of OCR and ECAR and metabolite flux in developing embryos. Oxygen (O₂) is consumed by respiring mitochondria in cells to support oxidative metabolism of multiple substrates. Hydrogen ions (H+) are exported from cells with lactate but can also be generated from CO₂ in the aqueous G-MOPS buffer or co-transported into cells along with pyruvate or lactate. The six carbons of glucose can be released as CO₂ during oxidative metabolism, as two lactate molecules following glycolysis, or utilized in the biosynthetic pentose phosphate pathway (PPP) and one-carbon metabolism (1CM) pathway.