Before revision:  The energetic cost for kinesin-1 varies nonmonotonically with ATP concentration and load (f) , and is locally minimized at [ATP] \approx 200 \muM and f\approx 4 pN. Remarkably,  this local minimum vanishes and the cost increases significantly for a mutant that has a longer neck-linker , which underscores the importance of molecular structure in transport properties.
After revision:  The energetic cost for kinesin-1 varies nonmonotonically with ATP concentration and load (f) , and is locally minimized at [ATP] \approx 200 \muM and f\approx 4 pN. Remarkably, for the mutant with a longer neck-linker this local minimum vanishes and the cost increases significantly for a mutant that has a longer neck-linker , which underscores the importance of molecular structure in transport properties.