Dr. Akabas and his colleagues wrote a paper on the amino acid residues lining the chloride channel of the cystic fibrosis transmembrane conductance regulator, or CFTR. By 1994, when this paper was published, the structures and functions of the cytoplasmic domains had been extensively studied, but very little was known about the 12 membrane-spanning segments and their relationship to the chloride channel. Mutations in some residues were also known to be associated with mild clinical disease, but the structural basis for these changes was unknown. Dr. Akabas devised his own method for identifying debris lining the canals and with it produced much new information. The team of scientists hoped to determine the structure of the channel-forming domains in CFTR. The key experiment, called the substituted cysteine ​​accessibility method, or SCAM, involved mutating and replacing 9 consecutive residues in the M1 membrane-spanning segment with cysteine ​​in Xenopus oocytes, or eggs. If the cysteine-mutated channels still functioned, then the structures of the mutated and normal channels were assumed to be similar. Next, they determined the accessibility of the cysteine ​​residue by adding the reagents MTSEA and MTSES, which are highly specific reagents that form a mixed disulfide with a free sulfhydryl that covalently links the reagent to the cysteine. In other words, if MTSEA and MTSES bind to the cysteine ​​residue and alter conduction, they can assume the accessibility of the residue and thus infer that the side chain of the corresponding wild-type residue, or the residue before substitution, lines the channel . This process was used to determine the ion change structures… in the middle of the paper… to allow the MTS reagents to reach those residues. This experiment confirmed the strong evidence that Arg-347 was aligned along the channel. Dr. Akabas also hypothesized that studies of CFTR would lead to discoveries and insights into the structures of their membrane-spanning domains. Akabas concluded his article with a summary of his findings. He concluded that Gly-91, Lys-95, and Gln-98 all flank the CFTR channel and are arranged in a helical formation. Dr. Akabas also talked about the problems and surprises he faced during his experiment, such as a missense mutation of Gly-91 to Arg. Ultimately, the substituted cysteine ​​accessibility method exceeded the expectations of many and contributed greatly to our knowledge of the CFTR channel. Even though more research and discoveries are being made today, we will always remember Dr. Akabas' experiment as the basis of CFTR science.