The polypeptide bradykinin is obtained by enzymatically processing a blood prote

Question

The polypeptide bradykinin is obtained by enzymatically processing a blood protein. Both the N- and C-terminal amino acids of bradykinin are arginine (Arg). In the laboratory, complete hydrolysis of bradykinin gives three proline (Pro), two arginine (Arg), two phenylalanine (Phe), one glycine (Gly), and one serine (Ser) amino acid. In another experiment, partial hydrolysis of bradykinin gives the following fragments: Gly-Phe-Ser-Pro; Pro-Phe-Arg; Ser-Pro-Phe; Pro-Pro-Gly; Pro-Gly-Phe; Arg-Pro-Pro; Phe-Arg. What is the primary structure of bradykinin?

Explanation / Answer

Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg

...because there are only 9 aminoacids in bradykinin, as suggested by molecular weight, and the arginine shows twice, in the N-terminus of a fragment, followed by 2 prolines, and in the C-terminus of 2 fragments, preceded by phenylalanine in both, with the proline preceded by a serine in the other. Then another fragment has serine-proline-phenylalanine. It must be that the C-terminus is Ser-Pro-Phe-Arg, and the N-terminus Arg-Pro-Pro, because the first experiment found only 2 arginines in the entire oligopeptide, and so on...

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