Transport of reducing equivalents: The inner mitochondrial mem- brane lacks an NADH transporter, and NADH produced in the cytosol cannot directly enter the mitochondrial matrix. However, two electrons of NADH (also called reducing equivalents) are transported from the cytosol into the matrix using substrate shut- tles. In the glycero phosphate shuttle (Figure 6.15A), two electrons are transferred from NADH to dihydroxyacetone phosphate by cytosolic glycero phosphate dehydrogenase . The glycerol 3-phos- phate produced is oxidized by the mitochondrial isozyme as FAD is reduced to FADH 2 . CoQ of the electron transport chain oxidizes FADH 2 . The glycero phos phate shuttle, therefore, results in the syn- thesis of two ATPs for each cytosolic NADH oxidized. This con- trasts with the malate-aspartate shuttle (Figure 6.15B), which produces NADH (rather than FADH 2 ) in the mitochondrial matrix and, therefore, yields three ATPs for each cytosolic NADH oxidized by malate dehydrogenase as oxaloacetate is reduced to malate. A transport protein carries malate into the matrix.