The monocarboxylate transporter (MCT) isoforms 4 and 1 mediate the co-transport of lactate and protons with a 1:1 stoichiometry across the plasma membranes of skeletal and cardiac muscle cells. The flux of lactate and protons mediated by the MCT plays an important role in muscle pH regulation and energy metabolism.
Vinnakota, K. C. and D. A. Beard. Kinetic analysis and design of experiments to identify the catalytic mechanism of the monocarboxylate transporter isoforms 4 and 1. Biophysical Journal 100(2):369-380, 2011.