1 A biochemist isolates a peptide hormone with the following

1. A biochemist isolates a peptide hormone with the following sequence ADSERNCOLVILLAWLpGVKVQCALLDRET Which of these residues could contribute a positive charge? (Assume the residues are numbered 1 through 30, left to right.) Which residues contribute a negative charge? Which residues can be connected by a disulfide bond?

Solution

Ans. Amino acid sequence: A D S E R N C Q L V I L L A W L P G V K V Q C A L L D R E T

1. Amino acids contributing positive charge = R, K          [Labeled bold]

Basic amino acids (R, K, H) bear a positive charge under normal phycological conditions.

2. Amino acids contributing negative charge = D, E         [Labeled underlined]

Acidic amino acids (D, E) bear a negative charge under normal phycological conditions.

3. Cysteine (C) may form disulfide bond another C residues placed adjacently in a protein.

[Labelled bold underlined]