Eloisa Atienza

Frances Jane Hermo

Nick Rainier Santos

April 20, 2009

Chemistry 40 Biochemistry

Evangeline Amor

Assignment #2: Proteins

Amino acid analysis of an octapeptide revealed the following composition:

2 Arg, 1 Gly, 1 Met, 1 Trp, 1 Tyr,1 Phe, 1 Lys.

The following facts were observed:

a. Edman degradation gave

b. CNBr treatment yielded a pentapeptide and a tripeptide containing phenylalanine.

c. Chymotrypsin treatment yielded a tetrapeptide containing a C-terminal indole amino

acid and two dipeptides.

d. Trypsin treatment yielded a tetrapeptide, a dipeptide, and free Lys and Phe.

e. Clostripain yielded a pentapeptide, a dipeptide, and free Phe.

What is the amino acid sequence of this octapeptide?

CNBr attacks the peptide bond of Met at the carboxylic group.

Gly – Arg – Lys – Trp – Met + Tyr – Arg – Phe

Chymostrypsin attacks the peptide bonds of amino acids with aromatic ring at the

carboxylic group.

Gly – Arg – Lys – Trp + Met – Tyr + Arg – Phe

Trypsin attacks the peptide bonds of Arginine and Lysine at the carboxylic group.

Gly – Arg + Lys + Trp – Met – Tyr – Arg + Phe

Clostripain attacks the peptide bond of Arginine at the carboxylic group.

Gly – Arg + Lys – Trp – Met – Tyr – Arg + Phe

Structure of the octapeptide:

Gly – Arg – Lys – Trp – Met – Tyr – Arg – Phe