Fig. 4.

Theoretical model showing three possible mechanisms of lactate production by domestic cat and cheetah spermatozoa, with NADH, lactate, and ATP generated from the metabolism of endogenous glycogen (blue), phospholipid (green), and/or extracellular pyruvate (purple). Common metabolic products or intermediates are illustrated in black. Dashed line indicates the possibility of intramitochondrial lactate formation. For clarity, all enzymes and certain metabolic products or intermediates are omitted from the figure. The absence of lactate in the starting medium is noted by an asterisk (*). SLC16A7, monocarboxylic acid transporter 2 (formerly MCT2); G3P, glycerol-3-phosphate; DHAP, dihydroxyacetone phosphate; M-A shuttle, malate-aspartate shuttle.