Problem 3, 135

Problem 3, 135 - (Assume a value of 110 for the average...

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Problem 3 a) The salt-loving bacterium Halobacterium halobium produces a purple pigment consisting of the protein bacteriorhodopsin ( M r 26,000). The color of the pigment is a result of the conjugation of a lysine residue of the protein to the chromophore 11-cis-retinal. The pigment is aggregated into purple patches in the cell membrane, where the protein acts as a light-activated proton pump energizing cell functions. X-ray analysis of the protein reveals seven parallel transmembrane α -helices, each of which traverses the 45A o thick bacterial membrane completely. Calculate the minimum fraction of bacteriorhodopsin that composes the membrane spanning helices, and explain the reason that this value is a minimum.
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Unformatted text preview: (Assume a value of 110 for the average weight of an amino acid residue.) b) A 660 mg sample of an oligomeric protein ( M r 132,000) was treated with an excess of dansyl chloride under slightly alkaline conditions in order to saturate available amino groups with the reagent. The labeled protein was subjected to acid hydrolysis, and the hydrolysate was found to contain 7.0 mg of dansyl-val as the only α-dansylated amino acid. Calculate the number of polypeptide chains in the oligomer, and suggest a technique for determining whether or not the polypeptides composing the protein are identical....
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