Simple Microassay of Protein with Membrane Filter

Abstract

THE quantity of protein in dilute solution is usually determined by the method of Lowry et al.¹, using phenol reagent. This method is sensitive and simple, but it is applicable only to solutions containing more than 10 µg/ml. and it suffers from interference by various chemicals. For example, tris(hydroxymethyl) aminomethane can react with the reagent to develop an intense colour and in the presence of magnesium ions the phenol reagent forms a precipitate which greatly lessens the strength of the colour. Thus unless freed from these materials the values obtained under these conditions are rather unreliable. Removal of the interfering chemicals cannot be easily performed with dilute protein solutions and is inconvenient if a large number of samples is being analysed. Protein determination by ultra-violet absorbancy may also suffer from severe interference by other chemicals. The reading is affected by nucleotides or many other chemicals and the results must be corrected for them².