Physical characteristics of human transferrin from small angle neutron scattering

The technique of small angle neutron scattering has been used to determine the molecular shape, the volume, and the molecular weight of pooled human transferrin in an aqueous solution isotonic with blood. Analysis of the measurements assuming a spheroidal molecular shape indicates that an oblate spheroid with semi-axes of length 46.6 +/- 1.4, 46.6 +/- 1.4 and 15.8 +/- 3.8 A, and a molecular volume of (144 +/- 45) X 10(3) A3 is the best simple approximation to the shape of the transferrin molecule. The radius of gyration, Rg, determined from a Guinier plot is 30.25 +/- 0.49 A, in agreement with Rg calculated for the oblate spheroidal shape. The molecular weight is determined to be (75 +/- 5) X 10(3). The shape-independent molecular volume is found to be (98 +/- 10) X 10(3) A3. The difference in the two volumes suggests that transferrin is not a uniform spheroid but may have a more complex shape.