Ferritin is a hollow iron-storage protein61 consisting of 24 subunits that are a variable mixture of heavy (H) or light (L) chains, arranged in octahedral symmetry. The hollow center, with a diameter of 8 nm, can hold up to 4 500 iron atoms in the approximate form of the mineral ferrihydrite (5Fe2O3 9H2O). Iron(II) enters the protein through eight pores located on the threefold symmetry axes of the octahedron. Oxidation to Fe(III) occurs at catalytic sites on the H chains. Other sites on the inside of the L chains
appear to nucleate the crystallization of ferrihydrite. Migration times for protein standards and the ferritin subunits are given in the table. Prepare a graph of log(molecular mass) versus 1/(relative migration time), where relative migration time (migration time)/(migration time of marker dye). Compute the molecular mass of the ferritin light and heavy chains. The masses of the chains, computed from amino acid sequences, are 19 766 and 21099 Da.

Transcribed Image Text:

Molecular mass (Da) Migration time (min) 13.17 16.46 18.66 20.16 22.36 23.56 24.97 28.25 17.07 17.97 Protein Orange G marker dye a-Lactalbumin Carbonic anhydrase Ovalbumin Bovine serum albumin Phosphorylase B B-Galactosidase Myosin Ferritin light chain Ferritin heavy chain 14 200 29 000 45 000 66 000 97 000 116 000 205 000 1