Promotion and suppression effects of cationic polymer ε-poly-L-lysine on the glucose oxidase reaction with ferrocene derivatives as oxidants with different charges

The effects of the cationic polymer ε-poly-L-lysine (εPL) on the enzymatic reaction rate of glucose oxidase (GOD) with ferrocene derivatives having different ionic charges have been investigated by measuring the ferrocene derivative-mediated catalytic current of oxidation by GOD. When negatively charged ferrocenes were used, the bioelectrocatalytic current, which is related to the enzymatic reaction rate, was increased by the addition of εPL. On the other hand, the reaction rates with positively charged ferrocenes were decreased by εPL. These promotion and suppression effects of εPL were remarkable at a certain pH range, where εPL and GOD were charged positively and negatively, respectively. Within this range, the polycationic εPL would be adsorbed onto the GOD surface to enhance the electrostatic interactions of the enzyme with negatively charged substrates, and repulsion with positively charged ones. These findings should be important for practical applications of enzymes.

Analytical methods for the detection and purification of ε-poly-L-lysine for studying biopolymer synthetases, and bioelectroanalysis methods for its functional evaluation

This article describes new analytical methods for studying biopolymer ε-poly-L-lysine (εPL). The produced amount of εPL in culture broth can be determined based on the precipitation of polycationic εPL with a colored heteropolymolybdate anion and the color change of the supernatant. The product can be separated and purified by precipitation with the tetraphenylborate anion and reprecipitation in the form of the hydrochloride salt. These methods have been applied advantageously to the screening of εPL-synthetase. Also, pyrophosphate can be determined colorimetrically based on the formation of 18-molybdopyrophosphate species. The pyrophosphate determination has been successfully applied to the assay of adenylation enzyme, which plays important roles in the biosynthetic mechanism. Under certain conditions, εPL associates with a redox enzyme, glucose oxidase. The effect of the adduction on the stability and reaction rate of the enzyme can be evaluated by measuring the bioelectrocatalytic current, which is related to the enzyme activity. Electrochemical studies showed new applications of εPL as an enzyme stabilizer and a reaction enhancer.