Molecular Weight, Single‐Chain Structure and Amino Acid Composition of Human Lactoferrin

Abstract

A molecular weight of 75000 was computed for human lactoferrin on the basis of a sedimentation coefficient s ° 20, W = 4.93, a partial specific volume v̄ 20 = 0.715 and a diffusion coefficient D ° 20, W = 5.6×10 −7 cm 2 xsec −1 . A molecular weight of 76800 ± 1600 was estimated from electrophoreses in agarose acrylamide gel containing sodium dodecylsulphate. No decrease of the molecular weight was observed when the reduced and alkylated or aminoethylated protein was submitted to 6 M urea, indicating that the molecule of lactoferrin consists of a single polypeptide chain. From the analysis of the amino acid composition of human lactoferrin a theoretical molecular weight of 76400 was computed by means of a statistical test. A comparison of the amino acid compositions of human lactoferrin and transferrin suggests that the two proteins are more closely related to one another than was suspected before.