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.

VQSYEKEEDLLQAWSTFIRIMDPDVITGYNIQNFDLPYLISRAQTLKVQTFPF

Amino acids have characteristic titration curves. A plot of the titration of an amino acid with a strong base resulted in just two distinct regions of greatest buffering power. This would likely be indicative of an amino acid with:

The image below is a representation of an acid-base titration of a diprotic amino acid, labelled at specific points (i through v).

Which region represents where this amino acid's net charge is zero?

Mass spectrometry is a useful technique to sequence proteins. This typically initially involves:

A sample containing an unknown polypeptide of 20 amino acids was assessed through a combination of Edman degradation and tryptic digest with mass spectrometry.

The Edman degradation result showed a peptide sequence of: MRNNAGKA

The tryptic digest and mass spectrometry result showed peptide sequences of: 

TDDNVLLL and MR and NNAGK and ANFSR

What is the complete polypeptide sequence?

(Use the single letter amino acid code, with no spaces or non-amino acid characters)

The image below is a representation of an acid-base titration of a diprotic amino acid, labelled at specific points (i through v).

Which region corresponds to the pH being equal to the pKa of the carboxyl group?

In attempting to define the subunit composition of an unknown protein, you decide to subject the protein to SDS-PAGE in the presence or absence of the reducing agent DTT. The results of this analysis are shown below.

Lane 1: molecular weight marker ladder.

Lane 2: protein sample without DTT

Lane 3: protein sample with DTT.

From this analysis, what is the subunit composition of the original native protein?

Consider that you wish to separate a mixture of glutamate, glycine and lysine by ion exchange chromatography.

Using an anion exchange column at pH 5, which amino acid would you expect to elute first and which last?

pKa and pI values are as follows:

Glutamate: pK₁ = 2.19, pK₂ = 9.67, pK_R = 4.25, pI = 3.22

Glycine: pK₁ = 2.34, pK₂ = 9.62, pI = 5.97

Lysine: pK₁ = 2.18, pK₂ = 8.95, pK_R = 10.53, pI = 9.74

A sample containing an unknown polypeptide of 20 amino acids was assessed through a combination of Edman degradation and tryptic digest with mass spectrometry.

The Edman degradation result showed a peptide sequence of: MIYRALTKVA

The tryptic digest and mass spectrometry result showed peptide sequences of: 

LLTGK and AQ and VAAAR and ALTK and MIYR

What is the complete polypeptide sequence?

(Use the single letter amino acid code, with no spaces or non-amino acid characters)

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.

VPLSYLLSRGQQVKVVSQLLRQAMHEGLLMPVVKSEGGEDYTGATVIGPLKGVPPQD