# Determining Protein Molecular Weight and Tryptophan Residues

## How can we calculate the minimum molecular weight of the protein based on the given data?

a. By determining the weight percentage of tryptophan in the protein

## How many tryptophan residues are present in a molecule of the new protein?

b. Use the molecular weight estimate from size-exclusion chromatography to find out

## Answer:

The minimum molecular weight of the protein is 2040 Daltons and it contains 262 tryptophan residues.

## Explanation:

a. The minimum molecular weight of the protein can be calculated by dividing the weight percentage of tryptophan by the weight of tryptophan (0.48% / 0.0048 = 10). Therefore, the minimum molecular weight of the protein is 10 times the molecular weight of tryptophan, which is 10 x 204 = 2040 Daltons.

b. To determine the number of tryptophan residues in the protein, we can use the molecular weight estimate from the size-exclusion chromatography (53500 Daltons). Divide the molecular weight estimate by the molecular weight of tryptophan (53500 / 204 = 262.25). Since we can't have a fraction of an amino acid residue, we round down to 262 tryptophan residues in a molecule of the new protein.