Figure 2. Glucose fuels both ROS scavenging and ROS production.

Glucose metabolized through the hexose monophosphate shunt provides reducing equivalents for regenerating NADPH from NADP⁺. NADPH in turn is used by glutathione reductase (GR) to regenerate glutathione (GSH) from glutathione disulfide (GSSG). GSH is used for enzymatic and non-enzymatic scavenging of ROS, and for repair of proteins that have been oxidized by ROS. However, NADPH derived from the hexose monophosphate shunt is also a requisite cofactor for the production of nitric oxide (NO^·) by nitric oxide synthase and superoxide (O₂^·) by NADPH oxidase (NOX). Glucose metabolized through glycolysis provides reducing equivalents for regenerating NADH from NAD⁺. These reducing equivalents (electrons) normally transit the mitochondrial electron transport chain in the process of generating CO₂ and ATP, but under some conditions a substantial fraction of these electrons are instead captured by oxygen to form superoxide. (Adapted from (Robbins and Swanson 2014).