Albumin circulates freely in human plasma. while aquaporins, act as a channel for water to enter and exit the cell. Based on their physiological locations, how would the tertiary structure of these two proteins? Also suggest the amino acids on these proteins contains.
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Functional characterization of the first aquaporin membrane protein was reported in 1992, but most membrane physiologists felt that there must be openings (pores or channels) in cell membranes to permit a flow of water, because the osmotic permeability of some epithelial cells was much too large to be accounted for by simple diffusion through the plasma membrane. It is predicted that a single human aquaporin-1 channel protein facilitates water transport at a rate of roughly 3 billion water molecules per second. Such transport appears to be bidirectional, in accordance with the prevailing osmotic gradient.
In 1992 a "water channel" was identified and what its molecular machinery might look like was suggested; that is, proteins were identified that formed an actual channel in membranes that facilitated water movement.
In the mid-1980s Peter Agre, M.D. (professor of Biological Chemistry and Medicine - John Hopkins Med School - 2003 Nobel Laureate in Chemistry) studied various membrane proteins isolated from the red blood cells. He also found one of these in the kidney cells. Having determined both its peptide sequence and the corresponding DNA sequence, he speculated that this might be the protein of the so-called cellular water channel. He termed this channel protein - aquaporin.
Agre tested his hypothesis that aquaporin might be a water channel protein in a simple experiment (fig. 1 - below). He compared cells which contained the protein in question with cells which did not have it. When the cells were placed in a water solution, those that had the protein in their membranes absorbed water by osmosis and swelled up while those that lacked the protein were not affected at all. Agre also ran trials with artificial cell membranes, termed liposomes, which are a simple lipid bound droplets of water. He found that the liposomes became permeable to water only if the aquaporin protein was implanted in their artificial membranes.
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