The molar mass of a protein from ultracentrifugation experiments

Example 11.1 J The molar mass of a protein from ultracentrifugation experiments 

The data from an equilibrium ultracentrifugation experiment performed at 300 K on an aqueous solution of a protein show that a graph of In c agcunst (r/cmy is a straight line with a slope of 0.729. The rotationcd rate of the centrifuge was 50 000 rotations per minute and b = 0.70. Calculate the molar mass of the protein. 

A molar mass (the mass per mole of molecules) of 4.4 kg mol corresponds to a molecular mass (the mass of one molecule) of 4.4 kDa. Be careful to use the unit dalton (Da) to denote molecular, not molar, mass. 

If a plot of In c against is linear, then the ratio (In Cj - In Ci)/(rl - rf) has the form of the slope of the line. In practice, ln(c/g cm ) is plotted against (r/cm) to give a dimensionless slope. It follows that 

It follows from eqn 11.3 with 1 cm = 10 m and the slope 0.729 that the molar mass is 

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