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AKProblemSet4 - Chemistry 114A 2007 Problem Set#4 1 Amino...

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Chemistry 114A, 2007 Problem Set #4 1. Amino acid analysis of a peptide revealed only seven different amino acids where concentrations of some amino acids are higher than the others: The following facts of a peptide were noted: A) Carboxypeptidase A treatment yielded the amino acid threonine B) One cycle of Edman analysis released the PTH-adduct of arginine C) Treatment with staphylococcal protease (Glu-C) yielded a tripeptide and hexapeptide D) Chymotrypsin treatment of the peptide released a pentapeptide and tetrapeptide. The peptapeptide when treated with cyanogens bromide two dipeptides and tyrosine is released. E) Treatment of tetrapeptide generated from chymotrypsin treatment with β -mercaptoethanol yielded two identical dipeptides What is the amino acid sequence of this peptide? A) The last amino acid is a Thr B) The first amino acid is an Arg C) Sequence of the two peptide are Arg-X-Glu and X-X-X-X-X-Thr Or Arg-X-X-X-X-Glu and X-X-Thr D) Arg-X-Glu-X-aaa (aromatic amino acid) and X-X-X-Thr Or Arg-X-X-aaa and X-Glu-X-X-Thr Because the pentapeide releases a free Tyr and two dipeptides, the sequence of the pentapetide is either Arg-Met-Glu-Met-Tyr or Arg-Met-X-Met-Tyr E) Since b-mercaptoethanol yielded two peptides, they must be disulfide linked. Cys-Thr Cys-X Since they are identical in sequence, the sequence of the dipeptide must be Cys-Thr. This also suggests that Glu must be present within the N- terminal pentapeptide (Arg-Met-Glu-Met-Tyr). The sequence of the peptide is Arg-Met-Glu-Met-Tyr-Cys-Thr Cys-Thr 2. A biochemist is attempting to separate a dimeric RNA-binding protein (protein X) from a mixture of 7 other proteins (proteins 1 to 7). These proteins
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have the following properties: pI Size (MW) Binds to RNA Protein 1 10.0 82,000 no Protein 2 3.8 21,500 no Protein 3 7.9 23,000 yes Protein 4 9.8 22,000 yes Protein 5 5.5 43,000 no Protein 6 6.0 110,000 no Protein 7 8.5 37,000 yes Protein x 10.1 65,000 yes Explain what type of separation techniques can be used to separate protein X from the mixture.
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