Novel Biocatalysts Based on Bromelain Immobilized on Functionalized Chitosans and Research on Their Structural Features

Enzyme immobilization on various carriers represents an effective approach to improve their stability, reusability, and even change their catalytic properties. Here, we show the mechanism of interaction of cysteine protease bromelain with the water-soluble derivatives of chitosan-carboxymethylchitosan, N-(2-hydroxypropyl)-3-trimethylammonium chitosan, chitosan sulfate, and chitosan acetate-during immobilization and characterize the structural features and catalytic properties of obtained complexes. Chitosan sulfate and carboxymethylchitosan form the highest number of hydrogen bonds with bromelain in comparison with chitosan acetate and N-(2-hydroxypropyl)-3-trimethylammonium chitosan, leading to a higher yield of protein immobilization on chitosan sulfate and carboxymethylchitosan (up to 58 and 65%, respectively). In addition, all derivatives of chitosan studied in this work form hydrogen bonds with His158 located in the active site of bromelain (except N-(2-hydroxypropyl)-3-trimethylammonium chitosan), apparently explaining a significant decrease in the activity of biocatalysts. The N-(2-hydroxypropyl)-3-trimethylammonium chitosan displays only physical interactions with His158, thus possibly modulating the structure of the bromelain active site and leading to the hyperactivation of the enzyme, up to 208% of the total activity and 158% of the specific activity. The FTIR analysis revealed that interaction between N-(2-hydroxypropyl)-3-trimethylammonium chitosan and bromelain did not significantly change the enzyme structure. Perhaps this is due to the slowing down of aggregation and the autolysis processes during the complex formation of bromelain with a carrier, with a minimal modification of enzyme structure and its active site orientation.

Sulfation of chitosan from Sepia kobiensis as potential anticoagulant and antibacterial molecule

The present work aimed to synthesis of chitin, chitosan and sulfation of chitosan from cuttlebone of cuttlefish Sepia kobiensis. Principally chitin was extracted through sequential processes of demineralisation and deproteinzation. Then chitosan was synthesized by a deacetylation and finally sulfated at semi-heterogeneous condition using chlorosulfonic acid in N,N-dimethylformamide. The synthesized macromolecules were characterized for its structural, physical and thermal (CHN, DDA, FT-IR, NMR, XRD, Viscometric analysis, SEM and DSC) properties. Apart from anticoagulant potential of the sulfated chitosan was tested using human plasma by means of activated partial thromboplastin time (APTT) and prothrombin time (PT). Further sulfated chitosan was tested for antibacterial potential by well diffusion method against eleven human pathogenic clinical isolates of both Gram positive and Gram-negative strains and minimum inhibitory concentrations (MIC) was calculated accordingly. The results of this study revealed the effectiveness of the sulfated chitosan at semi-heterogeneous conditions as a potent antibacterial and anticoagulant molecule.