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Microtubule sliding in reactivated flagella
Abstract:
Recent experimental studies of microtubule sliding in demembranated sea urchin sperm flagella are described. A local iontophoretic application of ATP to a Triton-extracted flagellum elicits a local bending response whose form is in exact conformity with the predictions of the sliding microtubule model. Cinematographic analysis of the microtubule sliding initiated by treating fragments of demembranated flagella with trypsin in the presence of ATP reveals that the speed of sliding is almost constant. This implies that the speed does not depend on the number of dynein arms participating in the generation of sliding force. The distribution of apparent sliding velocities indicates that there is no difference in sliding velocity among the doublets. The sliding velocity depends on MgATP concentration in a manner consistent with Michaelis-Menten kinetics. The sliding velocity of doublets in trypsin-treated axonemes is close to the maximum velocity of relative sliding taking place between adjacent doublets in beating flagella reactivated at the same MgATP concentration.
Insights
Sea urchin sperm flagella studies confirm the sliding microtubule model. Microtubule sliding speed is constant and independent of dynein arms, depending mainly on MgATP concentration.
Area of Science:
- Cell Biology
- Biophysics
- Molecular Motor Function
Background:
- The sliding microtubule model explains flagellar movement.
- Understanding the mechanics of microtubule sliding is crucial for flagellar motility.
Purpose of the Study:
- To experimentally validate the sliding microtubule model in sea urchin sperm flagella.
- To investigate the factors influencing microtubule sliding speed and force generation.
Main Methods:
- Using demembranated sea urchin sperm flagella.
- Local iontophoretic application of ATP to induce bending.
- Cinematographic analysis of trypsin-treated flagellar fragments with ATP.
Main Results:
- Local ATP application induced bending consistent with the sliding microtubule model.
- Microtubule sliding speed remained constant, independent of dynein arm participation.
- Sliding velocity showed Michaelis-Menten kinetics with respect to MgATP concentration.
Conclusions:
- Experimental results strongly support the sliding microtubule model for flagellar motility.
- Dynein arm number does not limit sliding speed; MgATP concentration is the key factor.
- Observed sliding velocities are comparable to those in actively beating flagella.