[Changes in the parameters of equilibrium binding of acidic dyes by contractile proteins during their functional...

A study was made of the equilibrium distribution of acidic dyes (Heliogen blue, Bromthymol blue, Bromphenol blue, Phenol red) between actomyosin threads (intact, contracted by ATP, or denaturated by heating) and the medium. The limits of dye sorption (A infinity) were shown to rise with the increase in their hydrophobia. The heat denaturation is accompanied with similar changes in all the dyes examined: i.e. with the increase in the limits of dye sorption and constant dissociation, and with the decrease in dye affinity to protein. The functional activity of contractile proteins acted upon with ATP is accompanied with different changes. For Heliogen blue these are like those during denaturation, whereas for Phenol red these are quite opposite: the limits of dye sorption and constant dissociation diminish, and the affinity to protein rises. Thus, during the heat denaturation the number of polar and non-polar groups accessible to dyes increases, whereas during functional activity only the number of non-polar bonds increases, and the quantity of polar bonds is seen reduced.