Different strategies for covalent immobilization of enzymes on hydroxyapatite: a comparative study

Immobilization of enzymes on insoluble supports is a well-established strategy to implement biocatalysis in industrial processes avoiding poor long-term stability and difficult recyclability of enzymes and enabling process intensification via continuous flow technologies. Greener alternatives compared to petrol-based expensive supports usually employed have been subject of investigation in recent years. Among these, hydroxyapatite (HAP) represents a suitable candidate thanks to its structural stability, non- toxicity, large surface area and ease of surface modification. As it can be sourced from waste, it fulfills also the circular economy model. Three model enzymes were chosen to test HAP as a support: a vanadium-dependent chloroperoxidase from Curvularia inaequalis (CiVCPO), a L-tyrosine decarboxylase from Lactobacillus brevis (LbTDC) and an R-selective transaminase from Thermomyces stellatus (TsRTA). The immobilization of these on commercial supports has been reported in the context of producing valuable APIs or natural products. Three different strategies for enzyme immobilization, different experimental conditions, and protein loading were tested to maximize the immobilization yield and the recovered activity (Figure 1). The enzymes were efficiently bound to the support and their recyclability was tested successfully.