274 



C. J. BROKAW 



lO^M I0" 4 M IO" 5 M 



CONCENTRATION OF ATP 

 Fig. 3. Effect of ATP concentration on the beat frequency of isolated 

 fiagella (two preparations). 



increase of beat frequency with ATP concentration has been attrib- 

 uted to a "plasticizing" effect of ATP. However, no significant dis- 

 cussion of how a plasticizing effect should be related to the parame- 

 ters of flagellar activity has been presented. The ATP effect may be 

 too valuable a clue to the mechanism of flagellar activity to be dis- 

 missed so readily. A plasticizing effect might mean that ATP de- 

 creases the internal viscosity of the fiagella. This possibility can be 

 examined by measuring the effect of viscosity on movement at differ- 

 ent ATP concentrations. Some preliminary results are shown in 

 Fig. 4. 



The results presented in Fig. 4 should lie on straight lines if an 

 equation of the form used in Fig. 2 is valid, and the intercept with 

 the abscissa represents the value of the equivalent internal viscosity. 

 If the action of ATP were a reduction in internal viscosity, a set of 

 three lines of equal slope and different intercept should result. In- 

 stead, the values indicated for the internal viscosity are roughly the 

 same at all three ATP concentrations. The major effect of ATP is a 

 change in the slope of the lines, which implies that more energy is 

 being made available to overcome internal and external viscous re- 

 sistances, as ATP concentration is increased. The validity of this 

 conclusion depends on the constancy of the amplitude of beat, which 

 has not yet been accurately measured. Since the rate of ATP dephos- 



