Ultracentrifugal and electrophoretic studies on the milk proteins

Abstract

IT is generally assumed that milk serum contains two different proteins: lactalbumin and lactoglobulin.However, Palmer [1934] recently isolated a crystalline, globulin-like protein from the albumin fraction of cow's milk.Recent ultracentrifugal studies by Philippil have shown the presence of at least three differenit proteins in milk serum: a protein of rather low molecular weight, isolated later on by Kekwick,' the lactoglobulin studied by Palmer [1934] and a protein with a molecular weight higher than that of the latter.Recent investigations by the author gave similar results [Pedersen, 1936].This paper gives the result of an ultracentrifugal and electrophoretical study of the protein isolated by Palmer.The lactoglobulin used throughout this investigation was kindly put at the disposal of Prof. The.Svedberg by Prof. S0rensen.It was prepared by Dr Palmer at the Carlsberg Laboratory from cow's milk according to a modification of the method worked out by Dr Palmer himself.This preparation had been recrystallised four times.The material was received in Upsala as a wet crystal paste containing some toluene as preservative and was stored in this condition in the refrigerator (3-5°).A part of the lactoglobulin was later dried in a desic- cator over P205 and kept in the desiccator.These two materials behaved identi- cally in the centrifuge and in electrophoresis.At the end of this investigation a few experiments were carried out using another material prepared by R. A. Kekwick in Upsala according to the method of Palmer.The sedimentation values found for this material were identical with the earlier ones.The specific refraction increment and specific volume of lactoglobulin.2The determinations of the specific refraction increment were carried out on solutions I,,)