Cytochrome c adsorption on various poly-L-glutamic acid-containing calcium phosphate particles

Abstract

We synthesized novel materials at different temperatures with two types of poly-L-glutamic acid––poly-α-glutamic acid and poly-γ-glutamic acid––to confirm the effect of poly-L-glutamic acid, which exhibits hydroxyapatite (HAp) (pGlu-HAp) crystallinity, on particle morphologies and cytochrome c (Cyt c) adsorption abilities. Through hydrothermal treatment, rod-like particles, as well as thin sheet-like particles, grew along the c-axis. Moreover, the crystallinity of particles was found to improve with an increase in the reaction temperature from 60 ​°C to 120 ​°C. The Cyt c adsorption ability of pGlu-HAp, rather than the crystallinity of calcium phosphate, was affected by the peptide structure. Furthermore, pGlu–HAp was used effectively for Cyt c adsorption with not only the carboxyl residues of side chains in peptides but also mesopores in the range of 3–30 ​nm. In addition, the catalytic activity of Cyt c adsorbed on the particles containing poly-α-glutamic acid retained high activity and was similar to that exhibited by native free Cyt c. The graphene oxide/imogolite/Cyt c@pGlu-HAp-modified glassy carbon electrode showed good electrocatalytic responses as a candidate for a H2O2 biosensor. According to these results, the pGlu-HAp materials prepared in this study can act as useful enzyme carriers and electrodes, because they maintain high enzyme activity when adsorbed on particles.

Keywords

• Hydroxyapatite
• Poly-L-glutamic acid
• Crystallinity
• Porous structure
• Protein adsorption
• Cytochrome c