THE INFLUENCE OF 2,3-BUTANEDIONE 2-MONOXIME (BDM) ON THE INTERACTION BETWEEN ACTIN AND MYOSIN IN SOLUTION AND IN SKINNED MUSCLE-FIBERS

2,3-butanedione 2-monoxime (BDM) inhibits muscle contraction and actom yosin ATPase both in fibres and in solution. It is potentially useful as a tool for exploring weak interactions between actin and myosin. We have examined the effect of BDM on several key steps of the myosin su bfragment-1 and actomyosin subfragment-1 ATPase in solution. These stu dies show that BDM shifts the equilibrium between two actomyosin state s towards a more weakly bound form when the actomyosin complex has ADP alone or ADP and phosphate bound. We also confirm the findings of Her rmann and colleagues (1993, Biochemistry, 31, 12227-32) that the main effect of BDM on the myosin subfragment-1 ATPase is to slow the releas e of phosphate following ATP hydrolysis. Skinned fibre studies show th at the effects of BDM and phosphate on the steady isometric tension of the fibres are additive. This is consistent with the interpretation t hat BDM is reducing fibre tension either by increasing phosphate bindi ng or by a direct effect on the crossbridge. Tension transients induce d by rapid pressure release were examined in single muscle fibres; the y showed that BDM reduces the rate of tension generation following pre ssure release. This result suggest that BDM directly affects the force generating event in the crossbridge.