Enzymatic d-p-hydrophenyl glycine synthesis using chitin and chitosan as supports for biocatalyst immobilization

A novel process using immobilized engineered strain HC01 cells with co-expressed D-hydantoinase and D-N-carbamoylase as biocatalyst for the production of D-Valine

The demand for D-Valine increases because of its wide range of use. A whole-cell biocatalyst for the production of D-Valine from 5'-isopropyl hydantoin by co-expression of the D-hydantoinase (hyd) gene from Pseudomonas putida YZ-26 and D-N-carbamoylase (cab) gene from Sinorhizobium sp. SS-ori in Escherichia coli BL 21 (DE3) was developed. The expression condition of the engineered strain HC01 co-expressing D-hydantoinase (HYD) and D-N-carbamoylase (CAB) was optimized. HYD and CAB reached the highest activities (4.65 and 0.75 U/ml-broth) after inducing for 8-12 h. Subsequently, the cells of HC01 were immobilized in the form of Ca²⁺-alginate beads, and the optimal conditions for immobilizing were obtained as 2.5% gel concentration and 0.029 g/mL cell concentration in the presence of 3% CaCl₂. The thermostability of immobilized cells was 5 ℃ higher than that of free cells in the same condition. And the divalent metal ions such as Mn²⁺, Mg²⁺, Cu²⁺, Co²⁺, and Ni²⁺ did not significantly affect the enzymatic activity of HYD and CAB in immobilized cells. Bioconversion rate reached to 91% after a 42-h reaction when the substrate concentration was 50 mmol/L with the initial pH of 9.0 under the nitrogen protection. This method provides D-Valine with optical purity of 97% and an overall yield of 72%. Furthermore, the immobilized cells can be reused for more than 7 cycles and maintain their capacity of over 70%. Hence the immobilized cells of engineered strain HC01 could potentially be used to prepare D-Valine.

Chitosan: An Overview of Its Properties and Applications

Chitosan has garnered much interest due to its properties and possible applications. Every year the number of publications and patents based on this polymer increase. Chitosan exhibits poor solubility in neutral and basic media, limiting its use in such conditions. Another serious obstacle is directly related to its natural origin. Chitosan is not a single polymer with a defined structure but a family of molecules with differences in their composition, size, and monomer distribution. These properties have a fundamental effect on the biological and technological performance of the polymer. Moreover, some of the biological properties claimed are discrete. In this review, we discuss how chitosan chemistry can solve the problems related to its poor solubility and can boost the polymer properties. We focus on some of the main biological properties of chitosan and the relationship with the physicochemical properties of the polymer. Then, we review two polymer applications related to green processes: the use of chitosan in the green synthesis of metallic nanoparticles and its use as support for biocatalysts. Finally, we briefly describe how making use of the technological properties of chitosan makes it possible to develop a variety of systems for drug delivery.

Immobilization of Enzymes in Protein Films

Heterogeneous biocatalysis usually involves the use of immobilized enzymes on solid supports. Enzymes have suitable properties in terms of efficiency and selectivity for use as immobilized catalysts. Different approaches have been developed for effective immobilization, including adsorption, covalent binding, entrapment, encapsulation, and cross-linking. Those systems offer some advantages with regard to homogeneous catalysts in solution, such as low costs, easy separation and recovery of the catalyst, reusability, and enzymatic stability. Here, we describe a new approach for the immobilization of active enzymes into homogenous films composed solely of scaffolding proteins that differs from the standard methods of enzyme immobilization on solid supports.