Myosin V, a processive actin motor, is studied by the same three types of measurement…

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Molecular machines, transport and bioenergetics · Molecular machines, transport and bioenergetics

Forces, Machines and Signals, Ch Enzymes and molecular motors

Problem

Myosin V, a processive actin motor, is studied by the same three types of measurement as kinesin. ((a)) Its ATPase rate is measured at two ATP concentrations:

v=40\,\mathrm{s^{-1}}

[\mathrm{ATP}]=20\,\mathrm{\mu M}

, and

v=70\,\mathrm{s^{-1}}

[\mathrm{ATP}]=70\,\mathrm{\mu M}

. Find

k_{\rm cat}

and

K_M

. ((b)) At low, rate-limiting ATP the randomness parameter is measured to be

r=1.0

. How many rate-limiting sub-steps does this indicate? ((c)) Single-molecule traces show a head stays bound to actin for

300\,\mathrm{ms}

out of a

330\,\mathrm{ms}

mechanical cycle. Compute the duty ratio and state whether myosin V can walk alone.

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