Filament spacing, effect

Schoenberg, M., Geometrical factors influencing muscle force development 1. The effect of filament spacing upon axial forces, Biophys. J., 30,51 7,1980. 

Figure 4. The effect of pH on filament spacing. Relatice A-band volume (determined by light microscopic measurement of skinned fiber diameter) and interaxial separation (determined by low-angle x-ray diffraction of skinned fibers) plotted against the pH of the bathing medium which contained 200 mM potassium propionate, 1 mM magnesium chloride, 10 mM EGTA with the pH adjusted with propionic acid.

Origin Preferential evaporation of the lighter isotope from the sample filament Preferential radial deflection of lighter ions from the center of ion beam (Coulomb repulsion due to space charge effects of charged ions - loss in ion transmission)... 

There is considerable controversy over whether calponin and caldesmon interact on the same filament in vivo. In vitro, calponin competes with caldesmon for closely spaced sites on the actin molecule and there is evidence that the two do not complex on the same filament (Makuch et al 1991, Mezgueldi et al 1992), In addition, the inhibitory effects of calponin and caldesmon on actin-activated ATPase activity appear to be unaffected by each others presence. These observations seem to support ultrastructu-ral evidence that these proteins may localize to different actin filaments or different locations on the same filament (North et al 1994a, Makuch et al 1991) (see Section 4.2.2). 

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