The effect of reaction temperature on the activity of recombinant Arabidopsis L-isoAsp methyltransferases. Methyltransferase activity assays were performed as described under “Materials and Methods” at various temperatures over the range of 0 °C to 65 °C with rAtPIMT2αω (120 ng protein), rAtPIMT2ψ (1.7 µg protein), rAtPIMT2ω (1.6 µg), and rAtPIMT1 (70 ng protein), and rhPCMT (50 ng protein). The rAtPIMT2ψ and rAtPIMT2ω isozymes were purified in parallel and assayed in at least duplicate, as were rAtPIMT2αω and rAtPIMT1 except at a later date. rhPCMT was purified and studied separately. Error bars represent the standard deviation from the mean.