Question

A newly isolated protein was found to contain 0.833% methionine by weight upon amino acid analysis.A newly isolated protein was found to contain 0.833% methionine by weight upon amino acid analysis.A newly isolated protein was found to contain 0.833% methionine by weight upon amino acid analysis.(a) What is the minimum molecular weight for the protein (assuming only one Met residue per protein molecule)? (b) Gel filtration of the protein gave an estimated molecular weight of 5.0 × 104 g/mol. How many Met residues are in the protein? (Enter a whole number).

Answer 1

A) MW of methionine = 149.21 g/mol.

MW of H₂O = 18 g/mol.

Minimum molecular weight of protein = (MW of methionine - MW of H₂O) / % methionine

                 = [(149.21 - 18) / 0.833] x 100

                 = 15751.5 g/mol

B) Number of Met residues = Total mol weight / Minimum molecular weight of protein

     = 5 x 10⁴ /15751.5 = 3.17 = 3.