Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 5

AMPPNP and the Contraction Cycle. AMPPNP is the abbreviation for a structural analogue of ATP in which the third phosphate group is linked to the second by a CH 2 group instead of an oxygen atom. AMPPNP binds to the ATP-binding site of virtually all ATPases, including myosin. It differs from ATP, however, in that its terminal phosphate cannot be removed by hydrolysis. When isolated myofibrils are placed in a flask containing a solution of calcium ions and AMPPNP, contraction is quickly arrested.
(a)Where in the contraction cycle will contraction be arrested by AMPPNP Draw the arrangement of the thin filament, the thick filament, and a cross-bridge in the arrested configuration.
(b)Do you think contraction would resume if ATP were added to the flask containing the AMPPNP-arrested myofibrils Explain.
(c)What other processes in a muscle cell do you think are likely to be inhibited by AMPPNP