Actomyosin, a complex of actin filaments and myosin motor proteins, is resp
onsible for force generation during muscle contraction. To resolve the indi
vidual mechanical events of force generation by actomyosin, we have develop
ed a new Instrument with which we can capture and directly manipulate indiv
idual myosin subfragment-1 molecules using a scanning probe. Single subfrag
ment-1 molecules can be visualized by using a fluorescent label. The data t
hat we obtain using this technique are consistent with myosin moving along
an actin filament with single mechanical steps of approximately 5.3 nanomet
res; groups of two to five rapid steps In succession often produce displace
ments of 11 to 30 nanometres. This multiple stepping is produced by a singl
e myosin head during just one biochemical cycle of ATP hydrolysis.