Question

Name the protein that allows facilitated diffusion of water. What experiment demonstrated the function of this protein?

Short answer

The protein responsible for the facilitated diffusion of water is called Aquaporin. The function of this protein was demonstrated in an experiment conducted by Peter Agre and his colleagues in 1992. They isolated an unknown protein from red blood cells (named CHIP28), expressed it in frog eggs (Xenopus oocytes), and subjected the oocytes to an osmotic swelling assay. Oocytes with CHIP28 swelled rapidly in a hypotonic solution due to water influx, while control oocytes didn't. The water transport through CHIP28 could also be specifically inhibited by mercury, confirming its involvement in water transport. The protein was later renamed Aquaporin and found to play a vital role in water homeostasis in various tissues and species.

Step-by-step solution

Identify the Protein

The protein responsible for the facilitated diffusion of water is called Aquaporin.

Describe the Experiment

The experiment that demonstrated the function of aquaporin was conducted by Peter Agre and his colleagues in 1992. The experiment can be summarized in the following steps: 1. Isolation of proteins from red blood cells: Agre and his team initially discovered an unknown protein in red blood cells, which they named CHIP28 (channel-forming integral protein of 28 kDa). 2. Expression of CHIP28 in Xenopus oocytes: The researchers expressed the CHIP28 protein in frog eggs (Xenopus oocytes), which don't normally express this protein. 3. Osmotic swelling assay: The Xenopus oocytes expressing CHIP28 were subjected to an osmotic swelling assay. They were placed in a hypotonic solution and their behavior was compared to oocytes without the protein. The oocytes with CHIP28 swelled rapidly and burst due to water influx, while the control oocytes didn't show such behavior. 4. Inhibition of the water channel: The scientists also demonstrated that the water transport through the CHIP28 protein could be specifically inhibited by mercury (Hg2+), thus confirming the protein's involvement in water transport. These experiments led to the conclusion that the CHIP28 protein was responsible for facilitating water transport across the cellular membrane. Later, CHIP28 was renamed Aquaporin, and it was shown to be present in various tissues and species, playing a vital role in water homeostasis in living organisms.