Proton-coupled monocarboxylate transporter. Catalyzes the rapid transport across the plasma membrane of many monocarboxylates such as lactate, pyruvate, branched-chain oxo acids derived from leucine, valine and isoleucine, and the ketone bodies acetoacetate, beta-hydroxybutyrate and acetate. Functions as high-affinity pyruvate transporter (By similarity). Interacts with GRID2IP (By similarity). Interacts with EMB (By similarity). Interacts with BSG (By similarity). Belongs to the major facilitator superfamily. Monocarboxylate porter (TC 2.A.1.13) family.