Equilibrium Kinetics of D-Glucose to D-Fructose Isomerization Catalyzed by Glucose Isomerase enzyme from Streptomyces phaeochromogenus

Paradigm shift in xylose isomerase usage: a novel scenario with distinct applications

Isomerases are enzymes that induce physical changes in a molecule without affecting the original molecular formula. Among this class of enzymes, xylose isomerases (XIs) are the most studied to date, partly due to their extensive application in industrial processes to produce high-fructose corn sirups. In recent years, the need for sustainable initiatives has triggered efforts to improve the biobased economy through the use of renewable raw materials. In this context, D-xylose usage is crucial as it is the second-most abundant sugar in nature. The application of XIs in biotransforming xylose, enabling downstream metabolism in several microorganisms, is a smart strategy for ensuring a low-carbon footprint and producing several value-added biochemicals with broad industrial applications such as in the food, cosmetics, pharmaceutical, and polymer industries. Considering recent advancements that have expanded the range of applications of XIs, this review provides a comprehensive and concise overview of XIs, from their primary sources to the biochemical and structural features that influence their mechanisms of action. This comprehensive review may help address the challenges involved in XI applications in different industries and facilitate the exploitation of xylose bioprocesses.

From a Sequential Chemo-Enzymatic Approach to a Continuous Process for HMF Production from Glucose

Notably available from the cellulose contained in lignocellulosic biomass, glucose is a highly attractive substrate for eco-efficient processes towards high-value chemicals. A recent strategy for biomass valorization consists on combining biocatalysis and chemocatalysis to realise the so-called chemo-enzymatic or hybrid catalysis. Optimisation of the glucose conversion to 5-hydroxymethylfurfural (HMF) is the object of many research efforts. HMF can be produced by chemo-catalyzed fructose dehydration, while fructose can be selectively obtained from enzymatic glucose isomerization. Despite recent advances in HMF production, a fully integrated efficient process remains to be demonstrated. Our innovative approach consists on a continuous process involving enzymatic glucose isomerization, selective arylboronic-acid mediated fructose complexation/transportation, and chemical fructose dehydration to HMF. We designed a novel reactor based on two aqueous phases dynamically connected via an organic liquid membrane, which enabled substantial enhancement of glucose conversion (70%) while avoiding intermediate separation steps. Furthermore, in the as-combined steps, the use of an immobilized glucose isomerase and an acidic resin facilitates catalyst recycling.

Kinetics of glucose isomerization to fructose by immobilized glucose isomerase: anomeric reactivity of D-glucose in kinetic model

The substrate specificity of immobilized D-glucose isomerase (EC 5.3. 1.5) is investigated with an immobilized enzyme-packed reactor. A series of isomerization experiments with alpha-, beta-, and equilibrated D-glucose solutions indicates that beta anomer as well as alpha anomer is a substrate of the glucose isomerase at pH 7.5 and 60 degrees C. For substrate concentration of 0.028 mol l(-1) (1% w/v), the initial conversion rate of alpha-D-glucose was 43% higher than that with equilibrated glucose at the same concentration and 113% higher than beta-D-glucose conversion rate. This anomeric reactivity of glucose isomerase is mathematically described with a set of kinetic equations based on the reaction steps complying with Briggs-Haldane mechanism and the experimentally determined kinetic constants. The proposed reaction mechanism includes the mutarotation and the isomerization reactions of alpha- and beta-D-glucose with different rate constants.