Item

Abstract

1.

1. Splitting, tension and relaxing effect of nucleosidetriphosphate (NTP) are activated by magnesium ions.
2.

2. For each NTP the Mg++ requirement is the same for splitting and tension. The Mg++ requirement for the relaxing effect is much less.
3.

3. The amount of Mg++ required for hydrolysis and tension increases from ATP to GTP in the order With more complete Mg++ activation the development of tension decreases in the same order This also applies for the splitting (with the exception of acetyl-ATP).
4.

4. The extent of tension development always depends on the extent of the rate of splitting. It is thus immaterial whether or not the rates of splitiing are of varying magnitude since the splitting of the same NTP by Mg++ is activated to a varying extent. Only acetyl-ATP develops with equal splitting less tension than the other NTP's.
5.

5. The Mg++ requirement for the relaxing effect increases in the order: When the Mg++ activation is maximal the relaxing effect decreases in the same order.
6.

6. The diversity of the NTP succession for tension and splitting on the one hand and for the relaxing effect on the other shows that considerable tension and splitting is produced when the NTP concerned contains an NH2 group in the 6-positio — whether in the purine or the pyrimidine ring. The relaxing effect is by comparison greater with purine derivatives than with pyrimidine derivatives, independent of the presence of the NH2 group in the 6-position in the ring system.
7.

7. The relaxing effect and tension development, in contrast to splitting, are not activated by Ca++ ions.
8.

8. The “relaxing factor” (Marsh) works only in the presence of ATP in concentrations > 2 · 10−3M or of acetyl-ATP and CTP in concentrations < 8 · 10−3M.
9.

9. The “relaxing factor” does not, however, work in the presence of ITP, UTP and GTP in concentrations up to 10−2M.
10.

10. It is shown that the inter-action between actomyosin and NTP's does not depend on the fact that ATP is built up from the bound ATP of the actomyosin and the other NTP by means of nucleodiphosphokinase.