ADDITIVITY OF THE SLIDING VELOCITY OF ACTO-H-MEROMYOSIN INVITRO DRIVEN BY ATP AND GTP

The in vitro motility assay of the sliding velocity of acto-H-meromyos in driven by ATP and GTP was made according to the previous method.1) In the presence of 15 muM ATP (and in the absence of ATP regenerating system), the sliding velocity of the F-actin labeled with rhodamine-ph alloidin decreased gradually as the consumption of the added ATP proce eded. When GTP (2 mM) was added together with ATP (15 muM), the slidin g velocity of the labeled F-actin at initial stage was approximately e qual to the sum of the individual contributions of GTP and ATP. Striki ngly, however, the sliding velocity of the labeled F-actin in the pres ence of ATP and GTP did not show any decrease at least until 6 min. Th is means that the sliding velocity of the labeled F-actin exceeds the simple sum of the contributions of ATP and GTP. The phenomenon is very difficult to explain in terms of the current ideas on the sliding mec hanism of actomyosin.2),3)