| Popis: |
1. 1.|It is possible to obtain curves representing the dependence of the degree of saturation of G-actin and F-actin with ADP, IDP and CTP on the concentration of the free nucleotides. 2. 2.|The equilibrium of saturation for G-actin with the three nucleotides is immediately complete; it is a true equilibrium. 3. 3.|The equilibrium of saturation of F-actin with ADP and IDP becomes almost complete only after a 40-min period of ultrasonification. It is shown that the difference between the true equilibrium and that found after 40 min disappears after applying a small correction. 4. 4.|The equilibrium, however, between F-actin and CTP is only an ‘apparent’ one, because the CTP is changed into CDP after having entered the F-actin complex. It is considered probable that the apparent equilibrium closely resembles the true equilibrium. 5. 5.|Owing to the splitting of CTP during binding to F-actin, the equilibrium concentration of free CTP is not identical with the concentration found at the end of the experiment. How the approximately correct equilibrium concentration of CTP can be found in spite of this is deduced. 6. 6.|The G-actin denatures even in a 3-min experiment all the more, the less it is saturated with nucleotide. The denaturation reaches a value representing 70% of the G-actin at a degree of saturation 7. 7.|Neither the denatured G-actin nor the denatured F-actin binds nucleotide to a measurable extent. This is taken into consideration when calculating the amount of free nucleotide as the difference between the added and the bound nucleotide. 8. 8.|A discussion is given concerning the corrections necessary because of the presence of traces of contaminating nucleotides as well as because of the sites of F-actin which remain inaccessible during a 40-min period of ultrasonic vibration. 9. 9.|The affinity constants found for G-actin and for F-actin with ADP, IDP and CTP are given. 10. 10.|The affinity constants of both actins with respect to ATP, ITP and CTP are calculated from the constants for ADP, IDP and CTP using the known relative affinities of the different nucleotides for G-actin and F-actin. The affinity constant for ATP with G-actin is thus calculated to be approx. 4·107 and with F-actin to be approx. 1·107. |
