Sliding velocity and ATPase activity of actomyosin complex in the presence of urea solute

Kumemoto, R. and Hatori, K.

Department of Bio-system Engineering, Yamagata University


Urea molecule is known as a denaturant for unfolding of proteins and is also thought to perturb the interplay between a protein and water molecules. We examined a contribution of water environment to the function of actomyosin complex using a perturbing agent, urea.
Rhodamine-phalloidin-bound actin filaments were stable in the presence of urea at the concentration below 2.0 M. The sliding velocity of actin filaments on heavy meromyosin (HMM) was decreased with an increase of urea concentration and was completely suppressed by the presence of 1.0 M urea while actin filaments were kept bound to myosin heads.
The actin-activated ATPase activity of HMM was also decreased as the urea concentration was increased in the range of 0 - 1 M. On the other hand, ATPase activity of HMM without actin filaments was independent of this concentration. Actin concentration-dependency of ATPase activity revealed that in the presence of 0.5 M of urea Km was increased up to 2-fold and the maximum rate of ATP hydrolysis was decreased to 50 % compared with that in the absence of urea. Both the motility and ATPase activation of actomyosin complex were impaired by the presence of urea solutes at low concentration in which no crucial unfolding of actin and myosin molecules occurred.