Table 1 Km values of MCT chimaeras for L-lactate and pyruvate

The Km values reported were derived using either L-[14C]lactate uptake or by monitoring changes in intracellular pH with BCECF as described in the Experimental section. Data are given ±S.E.M. derived from the fit of the mean data to the Michaelis–Menten equation by non-linear least squares analysis. The n values given represent the number of separate eggs used for each substrate concentration. No L-[14C]lactate uptake data are provided for the MCT4/1 chimaera because the very high Km values required the use of high substrate concentrations for which the specific activity became too low to measure uptake of L-[14C]lactate accurately.

Km value (mM) using [14C] substrateKm value (mM) using BCECF
MCT formLactatePyruvateLactatePyruvate
MCT15.7±1.2 (n=16)1.2±0.2 (n=16)3.5*1*
MCT412.9±2 (n=16)103±28 (n=24)28*150*
MCT1/426.5±5.7 (n=16)8.9±2 (n=16)15.8±2.6 (n=7)8.5±1.9 (n=9)
MCT4/1209.2±71.9 (n=7)27.3±5.2 (n=8)
  • * BCECF data for MCT1 and MCT4 are taken from [6].