Immobolization of alkaline phosphatase on silk using diazo, adsorption, glutaraldehyde, and azide method: Optimum pH and properties of the conjugates

Silk Fibroin-Based Materials for Catalyst Immobilization

Silk fibroin is a widely and commercially available natural protein derived from silkworm cocoons. Thanks to its unique amino acid composition and structure, which lead to localized nanoscale pockets with limited but sufficient hydration for protein interaction and stabilization, silk fibroin has been studied in the field of enzyme immobilization. Results of these studies have demonstrated that silk fibroin offers an important platform for covalent and noncovalent immobilization of enzymes through serving as a stabilization matrix/support with high retention of the biological activity of the enzymes of interest. In the hope of providing suggestions for potential future research directions, this review has been written to briefly introduce and summarize key advances in silk fibroin-based materials for immobilization of both enzymes/biocatalysts (including alkaline phosphatase, β-glucosidase, glucose oxidase, lipase, urease, uricase, horseradish peroxidase, catalase, xanthine oxidase, tyrosinase, acetylcholinesterase, neutral protease, α-chymotrypsin, amylase, organophosphorus hydrolase, β-galactosidase, carbonic anhydrase, laccase, zymolyase, phenylalanine ammonia-lyase, thymidine kinase, and several others) and non-enzymatic catalysts (such as Au, Pd, Fe, α-Fe2O3, Fe3O4, TiO2, Pt, ZnO, CuO, Cu2O, Mn3O4, and MnO2).

Silk Fibroin: An Emerging Biocompatible Material for Application of Enzymes and Whole Cells in Bioelectronics and Bioanalytical Sciences

Enzymes and whole cells serve as the active biological entities in a myriad of applications including bioprocesses, bioanalytics, and bioelectronics. Conserving the natural activity of these functional biological entities during their prolonged use is one of the major goals for validating their practical applications. Silk fibroin (SF) has emerged as a biocompatible material to interface with enzymes as well as whole cells. These biomaterials can be tailored both physically and chemically to create excellent scaffolds of different forms such as fibers, films, and powder for immobilization and stabilization of enzymes. The secondary structures of the SF-protein can be attuned to generate hydrophobic/hydrophilic pockets suitable to create the biocompatible microenvironments. The fibrous nature of the SF protein with a dominant hydrophobic property may also serve as an excellent support for promoting cellular adhesion and growth. This review compiles and discusses the recent literature on the application of SF as a biocompatible material at the interface of enzymes and cells in various fields, including the emerging area of bioelectronics and bioanalytical sciences.

Immobilization of the Alkaline Phosphatase on Collagen Surface via Cross-Linking Method

BACKGROUND

Collagen, the most abundant protein in the human body, and as an extracellular matrix protein, has an important role in the fiber formation. This feature of the collagen renders establishment of the structural skeleton in tissues. Regarding specific features associated with the collagen, such as, formation of the porous structure, permeability and hydrophilicity, it can also be used as a biocompatible matrix in the enzyme engineering.

OBJECTIVES

The aim of the present study was to investigate the application of the type I collagen as a matrix for alkaline phosphatase immobilization using cross-linking method.

MATERIALS AND METHODS

The Alkaline phosphatase was covalently immobilized on collagen matrix by using 1-ethyl-3- (dimethylaminopropyl) carbodiimide hydrochloride (EDC). The source of the alkaline phosphatase was from the bovine intestinal mucous. After that, the activity of the immobilized enzyme was assayed under different experimental conditions.

RESULTS

The optimum pH was similar to that of the free enzyme, whereas the optimum temperature and thermal stability were shown some increments. The surface topography of the collagen matrix containing immobilized enzyme and ALP (Alkaline phosphatase) deficient was investigated by Atomic-force microscopy (AFM). Images that have been obtained applying AFM show significant differences between uncovered and immobilized enzyme- matrix surface topography.

CONCLUSIONS

Our findings suggest that type I collagen can be utilized as a matrix for alkaline phosphatase immobilization via cross-linking method.

Review physical and chemical aspects of stabilization of compounds in silk

The challenge of stabilization of small molecules and proteins has received considerable interest. The biological activity of small molecules can be lost as a consequence of chemical modifications, while protein activity may be lost due to chemical or structural degradation, such as a change in macromolecular conformation or aggregation. In these cases, stabilization is required to preserve therapeutic and bioactivity efficacy and safety. In addition to use in therapeutic applications, strategies to stabilize small molecules and proteins also have applications in industrial processes, diagnostics, and consumer products like food and cosmetics. Traditionally, therapeutic drug formulation efforts have focused on maintaining stability during product preparation and storage. However, with growing interest in the fields of encapsulation, tissue engineering, and controlled release drug delivery systems, new stabilization challenges are being addressed; the compounds or protein of interest must be stabilized during: (1) fabrication of the protein or small molecule-loaded carrier, (2) device storage, and (3) for the duration of intended release needs in vitro or in vivo. We review common mechanisms of compound degradation for small molecules and proteins during biomaterial preparation (including tissue engineering scaffolds and drug delivery systems), storage, and in vivo implantation. We also review the physical and chemical aspects of polymer-based stabilization approaches, with a particular focus on the stabilizing properties of silk fibroin biomaterials.