Elasticity of a two-dimensionally arranged myosin subfragment-1 (S1) was measured by using a surface forces apparatus. To prepare a two-dimensionally arranged S1-monolayer on a functionalized silver surface, we used genetically engineered Dictyostelium S1 molecules. A highly reactive cysteine residue was fused to the COOH-terminus using the recombinant DNA method. On the other hand, the maleimide groups was self-assembled onto a silver surface. Then the mutant S1 molecules were chemically bound to the functionalized silver surface at its COOH-terminus. This arrangement technique was necessary in order to create a stable S1-monolayer by chemical bond formation onto the silver surface. The occupied area of the single S1 on the silver surface was about 110 nm(2). In the interaction between the S1-monolayer and mica surfaces in aqueous solution, a long-range attractive force was observed. The elastic constants (stiffness and Young's modulus) of myosin S1 were evaluated from force-distance profiles in aqueous solution, using the Hertz theory. We found that the stiffness (or spring constant) and Young's modulus of S1 in the absence of nucleotide are 4.4 +/- 1.0 pN/nm and 0.71 +/- 0.16 GPa, respectively. (C) 1999 Academic Press.