The study suggests the existence of two calponin-binding sites on actin: one responsible for ATPase inhibition that is insensitive to S1, and another from which calponin is readily displaced by S1.
No immediate clinical implications; leaves open whether dual calponin sites modulate contractility in intact human muscle.
Calponin is a smooth-muscle thin-filament protein implicated in the regulation of contraction. Its binding to actin is a prerequisite for inhibition of actin-activated myosin MgATPase. Investigating the molecular mechanism of this inhibition, it was found that titration of acto-myosin subfragment 1 with calponin in the presence of either ADP or ATP does not displace weakly or strongly bound myosin subfragment 1 (S1) from actin. S1.ADP, however, is able to release about two-thirds of the calponin from saturated (equimolar) complexes of actin-calponin. The remaining calponin is sufficient for almost full inhibition of acto-S1 MgATPase activity. Bunding of actin filaments by calponin takes place at a higher ratio calponin/actin (above 1:3) and, therefore, is not responsible for inhibition of the ATPase. Bundle formation is inhibited by S1.ADP. These results suggest the existence of two calponin-binding sites on actin; one, that is insensitive to S1, which is responsible for inhibition of the ATPase, the other, from which calponin is readily displaced by S1.
No takes yet. Share an insight, caveat, or question.
Kołakowski et al. (1997) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: