This flavin-dependent dehydrogenase is an essential membrane enzyme, functioning at the central junction of glycolysis, respiration and phospholipid biosynthesis. In bacteria, the enzyme is localized to the cytoplasmic membrane , while in eukaryotes it is tightly bound to the outer surface of the inner mitochondrial membrane . In eukaryotes, this enzyme, together with the cytosolic enzyme EC 220.127.116.11
, glycerol-3-phosphate dehydrogenase (NAD+), forms the glycerol-3-phosphate shuttle by which NADH produced in the cytosol, primarily from glycolysis, can be reoxidized to NAD+ by the mitochondrial electron-transport chain . This shuttle plays a critical role in transferring reducing equivalents from cytosolic NADH into the mitochondrial matrix [7,8]. Insect flight muscle uses only CoQ10 as the physiological quinone whereas hamster and rat mitochondria use mainly CoQ9 . The enzyme is activated by calcium .