Interference of Mannose and Galactose in Glucose Assay by the Glucose Oxidase/Peroxidase Method

Objectives: Although the glucose oxidase (GOx) enzyme is produced by a variety of different organisms. The most commonly enzyme originates from the fungus Aspergillus Niger is widely implicated in glucose estimation. A. niger GOx enzyme should be highly sensitive and selective for glucose. However, GOx extracted from A. Niger may contain other enzyme impurities. Potential interfering agents as glucose epimers can impact the accuracy of results obtained by glucose oxidase- Peroxidase method.

Methods: Glucose epimers as galactose and mannose were in vitro screened for interference with glucose estimation by glucose Oxidase-Peroxidase method (GOx-POD) at concentrations similar to physiological concentrations of glucose. Furthermore, different concentrations of mannose and galactose calibration experiments were estimated by the enzymatic method implicated for glucose determination to understand the potential source and mechanism of interference from glucose epimers.

Results: Epimers of glucose as mannose and galactose can interfere with the glucose determination using the glucose oxidase/peroxidase (EC 1.1.3.4/1.11.1.7) (GOx-POD) method utilizing reduced o-Dianisidine as the oxygen acceptor chromogen. There was a linear relationship between the concentrations of mannose and glucose readings. Each 0.11 μmol/l of mannose in samples leads to an apparent increase of about 0.11 μmol/l of glucose. This interference in the GOx-POD method for glucose assay can occur in the in vitro experimental samples and cause over-estimation of the glucose. While the implicated enzymatic method glucose oxidase/peroxidase can detect only higher concentrations of galactose up to 0.275 μmol/l.

Conclusion: Under the conditions of in vitro measurement of glucose, using GOx-POD method, different concentrations of mannose (low and high) and while higher concentrations of galactose have a measurable interference. Mannose exhibited the highest interference during screening. Enzyme kinetic analysis conducted with galactose and mannose supported the notion that, the reactivity of GOx enzyme toward epimers of glucose and the presence of enzymatic impurities (such as galactose or mannose oxidase) are two potential sources for sugar interference with GOx. It is suggested that careful attention should be paid to the wide applicability of the GOx-POD method for glucose assay.