Figure 5.

Enzymatic activity of the SERCA1a reconstituted in various environments. The end product of this coupled-enzyme assay is the oxidation of NADH to NAD⁺, which is seen as the decrease in absorption at 340 nm (the top panel). In the bottom panel the activity of the enzyme in the L₃ phase is compared to its activity in micellar solutions of either β-OG (low activity), C₁₂E₈ (high activity), or in a medium mimicking the L₃ intermembrane space (I-S, dotted line, low activity). The latter measurement has been performed at an enzyme concentration of 0.1 μM corresponding to the threshold detection by FRAPP. All other measurements have been performed at 1 μM. ATP: adenosine triphosphate. ADP: adenosine diphosphate. NAD: nicotinamide adenine dinucleotide. PK: pyruvate kinase. PEP: phosphoenolpyruvic acid.