2-Chloro adenosine triphosphate as substrate for sea urchin axonemal movement

The 2-substituted ATP analog 2-Chloro ATP was tested for its capacity to support axonemal movement. The movement of sea urchin axonemes reactivated with 2-Cl ATP appeared very similar to that with ATP. Detailed waveform analysis indicated that bend angle and shear amplitude were not significantly different for ATP and 2-Cl ATP. Although wavelength differs at particular nucleotide concentrations, if normalized to the beat frequency, it is similar for ATP and 2-Cl ATP. The main difference in the movement with the two analogs was seen in beat frequency and sliding velocity. The Vmax for beat frequency and mean sliding velocity was lower for 2-Cl ATP. The apparent Km for beat frequency and sliding velocity was much lower for 2-Cl ATP. The ratio of these two effects, that is, (Vmax/Km) is higher for 2-Cl ATP. Thus 2-Cl ATP is a good substrate for axonemal movement. The significantly lower Km of 2-Cl ATP was also demonstrated by its ability to support oscillatory motion at concentrations below that for ATP. The observations identify the structures and conformation of substrate necessary to support axonemal movement.