Question

The duty ratio for a motor protein is defined as the fraction of time in each cycle of activity of the motor in which the head is bound with high affinity to its cytoskeletal track. Which of the following is reasonable given this definition?

A. Myosin V has a higher duty ratio than myosin II, because Pi release is the rate-limiting step in its cycle.
B. Myosin II has a higher duty ratio than myosin V, because Pi release is the rate-limiting step in its cycle.
C. Myosin V has a higher duty ratio than myosin II, because ADP release is the rate-limiting step in its cycle.
D. Myosin II has a higher duty ratio than myosin V, because ADP release is the rate-limiting step in its cycle.

Answer 1

Myosin V has a higher duty ratio than myosin II because it spends more time bound to the actin filament, as ADP release is the rate-limiting step in its cycle, thus prolonging the attachment duration in each cycle of activity.

Step-by-step explanation:

The duty ratio of a motor protein like myosin is an important parameter that defines the fraction of time a myosin head stays bound with high affinity to the actin filament during its activity cycle. Given that myosin V has been found to have a prolonged interaction with actin because the release of ADP is the rate-limiting step in its cycle, we can infer that myosin V has a higher duty ratio than myosin II. In contrast, myosin II releases inorganic phosphate (Pi) which leads to a quicker detachment from actin after the power stroke, implying a lower duty ratio compared to myosin V.

Therefore, the correct answer to the question is that myosin V has a higher duty ratio than myosin II, because ADP release is the rate-limiting step in its cycle (Answer C).