A newly isolated protein was found to contain 0.873% phenylalanine by weight upon amino acid analysis.
a. What is the minimum molecular weight for the protein (assuming only one Phe residue per protein molecule)?
b. Gel filtration of the protein gave an estimated molecular weight of 7.0 x 104 g/mol. How many Phe residues are in the protein? (Enter a whole number)
a. The minimum possible molecular weight for the problem means the protein has the lowest possible number of the amino acid in question. That means the smallest protein molecule that can have 1 Phe residue and would comprise 0.873% of the protein's total weight.
Remember that the molecular weight of Phe is 165.2g/mol. Another factor to be considered is the position of the amino acid. If Phe is in the middle of the peptide sequence, an OH and H will be remved from the C-side and the N-side, respectively due to the condensation reaction for the peptide's polymerization. The molecular weight contributed by Phe will thereby be significantly reduced by an amount equivalent to themolecular weight of water (18.0 g/mol), thus making the minimum weight of the protein less than what it would be if it is in the end of the sequence.