Question

Describe the membrane reconstitution experiment, which provided convincing evidence that the chemiosmotic theory was likely to be correct.

Short answer

Answer: The purpose of the membrane reconstitution experiment conducted by Efraim Racker and Walther Stoeckenius was to test the chemiosmotic theory, which explains how the electrochemical gradient across a biological membrane is used to generate ATP. The experiment supported the theory by demonstrating that when a proton gradient was established using light-driven proton transport across an artificial membrane, ATP synthesis occurred. The findings provided crucial evidence that the chemiosmotic theory accurately describes the processes by which biological systems convert energy from different sources to produce ATP.

Step-by-step solution

Understand the chemiosmotic theory

The chemiosmotic theory, proposed by Peter Mitchell, explains how the electrochemical gradient across a biological membrane is used to generate ATP. It suggests that the energy conserved by electron transport chains is stored as an electrochemical gradient of protons across the membrane, which is then used to drive ATP synthesis.

Provide the background of the membrane reconstitution experiment

Efraim Racker and Walther Stoeckenius conducted the membrane reconstitution experiment to test the chemiosmotic theory. They designed a simple biological membrane system that could harness the energy produced by light-driven proton transport to drive ATP synthesis, which is one of the processes that chemiosmotic theory aims to explain.

Set up the experimental system

Racker and Stoeckenius carefully designed an experimental system to test the chemiosmotic theory. They isolated two essential components from different sources: bacteriorhodopsin, a light-driven proton pump from Halobacterium halobium, and the ATP synthase complex from mitochondrial membranes. The system was constructed by incorporating both molecules into artificial phospholipid vesicles called liposomes.

Activate the light-driven proton pump

The next step in the experiment was to expose the liposomes containing bacteriorhodopsin to light. As bacteriorhodopsin is a light-driven proton pump, its activation moves protons from the interior of the liposomes to the outside, creating a proton gradient across the liposome membrane. Consequently, this process generates an electrochemical gradient, as the chemiosmotic theory postulates.

Measure ATP synthesis

After establishing a proton gradient across the membrane, ATP synthesis occurs if the chemiosmotic theory is correct. To verify this, the researchers measured the ATP levels inside the liposomes. They observed an increased synthesis of ATP in response to light, indicating that the proton gradient generated by bacteriorhodopsin was driving the ATP synthase to produce ATP. This experiment shows that the electrochemical gradient (in this case, generated by light-driven proton transport) can indeed power ATP synthesis.

Confirm the chemiosmotic theory

The membrane reconstitution experiment conducted by Racker and Stoeckenius supported the chemiosmotic theory's fundamental concepts. It demonstrated that the electrochemical gradient generated across a membrane from light-driven proton transport enables ATP synthesis. Their findings provided crucial evidence that the chemiosmotic theory accurately describes the processes by which biological systems convert energy from different sources to produce ATP.