The precipitation of peptides and proteins by lignosulphonic acids.

The precipitation of peptide- and protein-lignosulphonic acid complexes can be demonstrated and studied in agar plates in the form of precipitation zones. The effects on the precipitates caused by variations in incubation temperature, incubation time, concentration of the reagents and in pH in the mixture of reagents, are described, and the nature of the peptide-lignosulphonic acid bond is discussed. The central lysis zones which appeared in some precipitation zones were found to be probably caused by excess of lignosulphonic acids. The possibility of developing the agar precipitation method described as a direct micro quantitative procedure for the determination of certain lignosulphonic acids in aqueous solution is suggested.