Computational multiple steady states in enzymatically catalyzed oxidation of monophenols by tyrosinase in an isothermal CFSTR

Immobilization of tyrosinase on polyacrylonitrile beads: biodegradation of phenol from aqueous solution and the relevant cytotoxicity assessment

An economical and stabilized immobilized-enzyme method was developed for the removal of phenol in wastewater.

Applications of HRP-immobilized catalytic beads to the removal of 2,4-dichlorophenol from wastewater

Novel HRP-immobilized beads with the excellent catalytic activity were successfully fabricated to remove 2,4-dichlorophenol from wastewater.

Immobilization of tyrosinase on modified diatom biosilica: enzymatic removal of phenolic compounds from aqueous solution

Acid and plasma treated diatom-biosilica particles, were modified with 3-aminopropyl triethoxysilane (APTES), and activated with glutaraldehyde. Then, tyrosinase was immobilized onto the pre-activated biosilica by covalent bonding. The biosilica properties were determined using SEM, and FTIR. The enzyme system has been characterized as a function of pH, temperature and substrate concentration. Optimum pH of the free and immobilized enzyme was found to be pH 7.0. Optimum temperatures of the free and immobilized enzymes were determined as 35 and 45 °C respectively. The biodegradation of phenolic compounds (i.e., phenol, para-cresol and phenyl acetate) has been studied by means of immobilized tyrosinase in a batch system. The immobilized tyrosinase retained about 74% of its original activity after 10 times repeated use in the batch system. Moreover, the storage stability of the tyrosinase-biosilica system resulted excellent, since they maintained more than 67% of the initial activity after eighth week storage. Highly porous structure of biosilica can provide large surface area for immobilization of high quantity enzyme. The porous structure of the biosilica can decrease diffusion limitation both substrate phenols and their products. Finally, the immobilized tyrosinase was used in a batch system for degradation of three different phenols.

Spatial bistability generates hunchback expression sharpness in the Drosophila embryo

During embryonic development, the positional information provided by concentration gradients of maternal factors directs pattern formation by providing spatially dependent cues for gene expression. In the fruit fly, Drosophila melanogaster, a classic example of this is the sharp on-off activation of the hunchback (hb) gene at midembryo, in response to local concentrations of the smooth anterior-posterior Bicoid (Bcd) gradient. The regulatory region for hb contains multiple binding sites for the Bcd protein as well as multiple binding sites for the Hb protein. Some previous studies have suggested that Bcd is sufficient for properly sharpened Hb expression, yet other evidence suggests a need for additional regulation. We experimentally quantified the dynamics of hb gene expression in flies that were wild-type, were mutant for hb self-regulation or Bcd binding, or contained an artificial promoter construct consisting of six Bcd and two Hb sites. In addition to these experiments, we developed a reaction-diffusion model of hb transcription, with Bcd cooperative binding and hb self-regulation, and used Zero Eigenvalue Analysis to look for multiple stationary states in the reaction network. Our model reproduces the hb developmental dynamics and correctly predicts the mutant patterns. Analysis of our model indicates that the Hb sharpness can be produced by spatial bistability, in which hb self-regulation produces two stable levels of expression. In the absence of self-regulation, the bistable behavior vanishes and Hb sharpness is disrupted. Bcd cooperative binding affects the position where bistability occurs but is not itself sufficient for a sharp Hb pattern. Our results show that the control of Hb sharpness and positioning, by hb self-regulation and Bcd cooperativity, respectively, are separate processes that can be altered independently. Our model, which matches the changes in Hb position and sharpness observed in different experiments, provides a theoretical framework for understanding the data and in particular indicates that spatial bistability can play a central role in threshold-dependent reading mechanisms of positional information.