Thermal stability, glucose oxidase

Some of the chemical and immunological properties of the D-glucose oxidases from A. niger and Penicillium glaucum have been compared. Although c.d. spectroscopy indicated that the protein chains have essentially identical conformations, small variations in their structures were revealed by differences in the thermal stabilities, catalytic properties, and immunological activities of the enzymes. 

Hydrogen peroxide is a by-product in the treatment of food with glucose oxidase. It is added to food in some specific canning procedures. An example is the pasteurization of milk with H2O2, which is important when the thermal process is shut down by technical problems. Milk thus stabilized is also suitable for cheesemaking since the sensitive casein system is spared from heat damage. The excess H2O2 is then eliminated by catalase. 

Glucose oxidase presence in honey is also derived from bees. Its optimum pH is 6.1. The enzyme oxidizes glucose (100%) and mannose (9%). The enzymatic oxidation by-product, hydrogen peroxide, is partly responsible for a bacteriostatic effect of nonheated honey, an effect earlier ascribed to a so-called inhibine . The enzymatic oxidation yields gluconic acid, the main acid in honey. Glucose oxidase activity and thermal stability in honey vary widely (limit values were given in Ta-... 

To avoid interference with the active site of the enzyme, D-glucose oxidase from Aspergillus niger has been immobilized by way of its carbohydrate moieties. Thus, treatment of the periodate-oxidized enzyme with a styrene derivative afforded a water-insoluble material retaining full enzymic activity and exhibiting enhanced thermal stability at 60 °C. 

As far back as the first publication of Braun and his coworkers on the successful bioencapsulation of enzymes in silicates [82], it was noted that sol-gel encapsulation stabilizes the proteins and provides protection against thermal denaturation. This was confirmed by a large number of authors for a wide range of bioentities (e.g., [84,85,254-255]). Notably, Heller s group reported a 200-fold stability increase of glucose oxidase by encapsulation in monolithic silica [256]. 

Zhang Y, Rochefort D. Activity, conformation and thermal stability of laccase and glucose oxidase in poly(ethyleneimine) microcapsules for immobilization in paper. Process Biochem 2011 46 993-1000. 

---