Colorimetric method to detect ε-poly-L-lysine using glucose oxidase

We describe a new colorimetric assay method using glucose oxidase (GOx) to detect epsilon-poly-L-lysine (epsilon PL). This method uses epsilon PL's remarkable effect of promoting the enzymatic reaction of GOx with ferricyanide ion. This reaction reduces ferricyanide ion to ferrocyanide ion, accompanied by a color change from yellow to colorless. In this colorimetric assay, the detection limit of epsilon PL was estimated to be approximately 0.5 mg/L when purified epsilon PL samples were used. epsilon PL has usually been produced by a fermentation process using Streptomyces albulus species. The components of the culture broth showed interference effects against the assay method. However, due to the high sensitivity of the assay method for epsilon PL, epsilon PL could be detected in the culture broth without any pretreatment. The detectable concentration of epsilon PL in the culture broth, c(PL,ac), was estimated to be approximately 20 mg/L. By combining the Berlin blue reaction with this method, the c(PL,ac), was reduced to 10 mg/L. In light of the proposed method's simplicity and sensitivity, it could be useful for screening epsilon PL synthetic enzymes and microorganisms. (C) 2016, The Society for Biotechnology, Japan. All rights reserved.