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] substrate | Km value (mM) using BCECF | |||
|---|---|---|---|---|
| MCT form | Lactate | Pyruvate | Lactate | Pyruvate |
| MCT1 | 5.7±1.2 (n=16) | 1.2±0.2 (n=16) | 3.5* | 1* |
| MCT4 | 12.9±2 (n=16) | 103±28 (n=24) | 28* | 150* |
| MCT1/4 | 26.5±5.7 (n=16) | 8.9±2 (n=16) | 15.8±2.6 (n=7) | 8.5±1.9 (n=9) |
| MCT4/1 | − | − | 209.2±71.9 (n=7) | 27.3±5.2 (n=8) |
*BCECF data for MCT1 and MCT4 are taken from [6].