Die nukleosidtriphosphatase-aktivität von L-Myosin und aktomyosin in abhängigkeit von den ionalen bedingungen

Abstract

1. 1. The dependence of nucleosidetriphosphatase (NTPase) activity of actomyosin and L-myosin on the ionic conditions has been investigated. 2. 2. The following holds with regard to the NTPase activity of calcium-activated L-myosin: 2.1. (a) Ca ions activate much more strongly the splitting of 6-OH-NTP by L-myosin gel and L-myosin sol than the splitting of 6-NH 2-NTP. 2.2. (b) The order in which the 6-OH-NTP is split at an increasing speed is very markedly dependent on the ionic strength. 2.3. (c) The order in which the 6-NH 2-NTP is split is independent of the ionic strength. ATP is always split more rapidly than CTP. 2.4. (d) All the NTPs are split more rapidly by L-myosin gel than by L-myosin sol. 3. 3. The following holds with regard to NTPase activity of L-myosin in the presence of magnesium ions: 3.1. (a) In the presence of Mg ++ the rates of splitting by L-myosin are low (< 0.1 μmole P × mg protein −1 × min −1). 3.2. (b) Mg ions activate the splitting of guanosine triphosphate (GTP) and inosine triphosphate (ITP) by gel and sol. The splitting of uridine triphosphate (UTP) and cytidine triphosphate (CTP) by the gel is only insignificantly altered. The splitting of both NTPs by the sol is inhibited by magnesium. The splitting of adenosine triphosphate (ATP) is always inhibited by Mg ions. 3.3. (c) The rate at which L-myosin gel and L-myosin sol split NTP decreases in the order: GTP > ITP > UTP > CTP ≳ ATP 3.4. (d) The order of the rate of splitting of NTP is independent of the ionic strength. With increasing ionic strength the rates decrease only slightly. 4. 4. In the absence of alkaline earth and in the presence of chelating agents L-myosin sol splits 6-NH 2-NTP more rapidly than 6-OH-NTP. 4.1. (a) Without addition of alkaline earth the rates for all NTPs are low. 4.2. (b) Addition of chelating agents activates the splitting of ATP and CTP very strongly and the splitting of UTP only slightly. The splitting of ITP and GTP is inhibited. 5. 5. The NTPase activity of actomyosin gel is fundamentally different from that of actomyosin sol and L-myosin preparations. 6. 6. Both in the absence of alkaline earth and in the presence of Mg and Ca, the gel splits NTP at a decreasing rate in the order ATP ≳ CTP > UTP > ITP > GTP. Splitting of all the NTPs, with the exception of ATP, is more strongly activated by 10 −3 M Mg ++ than by 10 −2 M Ca ++. EDTA inhibits the splitting of all NTP by actomyosin gel. 7. 7. When the ionic strength increases from 0.1 to 0.4 μ the NTPase activity of actomyosin gel becomes converted to the NTPase activity of actomyosin sol. 8. 8. At an ionic strength of 0.4 μ, in the presence of Mg ++, all the NTPs dissociate actomyosin. The dissociated L-myosin has the same NTPase activity as the L-myosin sol. 9. 9. When no Mg ++ is added the actomyosin sol is dissociated completely only by ATP. CTP causes a stronger partial dissociation than UTP. ITP and GTP are ineffective. 10. 10. In the absence of alkaline earth and in the presence of Ca, the ATPase and CTPase activities of actomyosin and L-myosin sol are therefore equal and the UTPase activity of both proteins is very similar. 11. 11. When no alkaline earth is added ITP, GTP and UTP are split by the undissociated actomyosin sol and the L-myosin sol at a similar low rate. 12. 12. In the presence of Ca ++, GTP is split more rapidly than ITP by actomyosin sol-NTPase, while ITP is split more rapidly than GTP by L-myosin-NTPase. 13. 13. All NTPs are split more slowly by actomyosin sol than by L-myosin sol. 14. 14. In the presence of EDTA also, ATP dissociates actomyosin completely. UTP, ITP and GTP do not bring about dissociation in EDTA-containing actomyosin sol. 15. 15. The EDTA-activation of the ATP-splitting by actomyosin sol is less than that by L-myosin sol. UTP-, ITP- and GTP-splitting by undissociated actomyosin sol is inhibited by EDTA.