The following peptide sequence was deemed too long to be easily assessed by mass spectrometry. Therefore, it was first digested with trypsin. In the box below, enter the amino acid sequence (use the single letter code; do not enter spaces or non-amino acid characters) of any ONE possible tryptic peptide that may have been detected by the mass spectrometer.

IDISQLVITKELTRAASDYAGKQAHVELAERMAGLDPGSAPSLGDRVPYV

Proteins can be separated according to their net charge. Which type of separation technique would result in positively charged proteins being eluted earlier than negatively charged proteins?

Q9. What would happen if the column was allowed to run dry?

Q8. Why would it be important to apply the protein sample very carefully to the column?

Q1. What is the fractionation range (MW) for proteins when using Sephadex G100?

Consider the following peptide sequence:

GSQANVMLTIHWEDCA

This peptide will be proteolytically cut by chymotrypsin, but not by trypsin.

What single amino acid substitution could you make that would prevent this peptide being cut by chymotrypsin but enable it to be cut by trypsin?

Consider the following peptide sequence:

ACDEGHIKLMGNPQST

This peptide will be proteolytically cut by trypsin, but not by chymotrypsin.

What single amino acid substitution could you make that would prevent this peptide being cut by trypsin but enable it to be cut by chymotrypsin?

Consider the following peptide sequence:

MVNNPQSTACDEGHIKL

This peptide will be proteolytically cut by trypsin, but not by chymotrypsin.

What single amino acid substitution could you make that would prevent this peptide being cut by trypsin but enable it to be cut by chymotrypsin?

An eager young biochemist was digesting the same protein in three different tubes. Each tube had a separate protease:

• trypsin
• chymotrypsin, which cleaves at the carboxyl side of the three large and bulky aromatic amino acids
• Glu-C, which cleaves C-terminally to Glu or Asp

After digestion, the samples were analysed by mass spectrometry but -- oh no! -- the biochemist forgot to label their tubes.

Luckily, they have you to help them.

Look at the sequences from each sample below to deduce (if possible) which enzyme had been used in which tube.