DYNAMIC LASER-LIGHT SCATTERING STUDIES OF THE EFFECTS OF PYROPHOSPHATE ON CYCLIC MOTIONS OF CROSS-BRIDGES IN ISOLATED THICK MYOFILAMENTS FROM LIMULUS STRIATED-MUSCLE

Pyrophosphate (PPi) is a non-hydrolyzable ATP analogue known to affect the binding between myosin heads and actin. By using a dynamic laser light scattering method, we have shown that 1-2 mM PPi enhances the in crease in ($) over bar Gamma values induced by Ca2+ in isolated thick myofilaments from Limulus striated muscle. However, similar treatment has no effect on the ($) over bar Gamma values of filaments suspended in either relaxing solution or ATP-free solution. ($) over bar Gamma i s the average linewidth of the photoelectron count autocorrelation fun ction of the light scattered. PPi had no effect on the increase of ($) over bar Gamma values by Sr2+ but it substantially increased the ($) over bar Gamma values of the thick myofilaments suspended in Ba2+-subs tituted Ca2+ activating solution. The results show that PPi also affec ts the energy-requiring cyclic cross-bridge motions.