The researchers also found a way to extend the lifetime of the dye from a few seconds to several minutes. Then they teamed up with physiology professor Yale Goldman and postdoctoral researcher Joseph Forkey, both at the University of Pennsylvania, in applying the technique to measuring myosin movement.
"First, we attach a little fluorescent dye to one of the feet and we take a picture with a digital camera attached to a microscope to find exactly where the dye is," Selvin said. "Then we feed the myosin a little food called adenosine triphosphate, and it takes a step. We take another picture, locate the dye, and accurately measure how far the dye moved."
By looking at the step size, the scientists can tell whether the protein is walking or inchworming along, Selvin said. If it is walking, the rear foot takes twice as big a step than if it were inchworming.
"The long dye lifetime allowed us to measure many consecutive steps, which occurred about once every 3 seconds," Selvin said. "The foot wearing the dye would move forward 74 nanometers, then pause while the unlabeled foot moved forward. The cycle would then repeat itself. The 74-nanometer step size we measured is consistent with a hand-over-hand walking mechanism and inconsistent with an inchworm mechanism."
As an additional check, the researchers also labeled the myosin higher up on the leg, "somewhere in the neighborhood of the thighbone," Selvin said. "The steps alternated in size between long and short, just as yo
Contact: James E. Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign