Covalent Immobilization of Different Enzymes on Hydroxyapatite, an Alternative Green Support

Greener and cheaper alternatives to petrol-based supports have been studied in recent years to implement biocatalysis in industrial processes exploiting enzyme immobilization. Among these, hydroxyapatite (HAP) represents a suitable candidate thanks to its structural stability, nontoxicity, large surface area, and ease of surface modification. As it can be sourced from waste, it also fulfills the circular economy principles. This work explored the use of HAP for covalent immobilization using three model enzymes: a vanadium-dependent chloroperoxidase from <i>Curvularia inaequalis</i> (<i>Ci</i>VCPO), an l-tyrosine decarboxylase from <i>Lactobacillus brevis</i> (<i>Lb</i>TDC), and an <i>R</i>-selective transaminase from <i>Thermomyces stellatus</i> (<i>Ts</i>RTA). Different strategies were tested, and derivatization with (3-aminopropyl)-triethoxysilane (APTES) followed by glutaraldehyde activation was found to be the most widely applicable. <i>Lb</i>TDC and <i>Ts</i>RTA immobilized through this strategy were tested in multiple reaction cycles to assess their stability and reusability, with promising results.