BIOMOLECULAR ASPECTS OF SPERMATOZOAN MOTILITY 205 



merit, and these were all useful for subsequent experiments. Similar 

 preparations, made in the same way from low concentrations of pro- 

 tein from the alkaline-salt extract of fish and rabbit muscles, were 

 used for controls. 



Gel specimens made in this way from flagella varied in their re- 

 activity, some responding to ATP and electrolytes several weeks after 

 preparation, others showing little or no activity even when freshly 

 made. The behavior of the gels was studied in open pools of reagents 

 on glass slides or in sealed cells. The results were recorded as optical 

 micrographs or on 16-mm film in cinephotomicrographic equipment 

 at 8 or 16 frames/sec or with time lapse up to 1 frame every 15 sec. 



STRUCTURE AND PROPERTIES OF GELS 



The floe thrown down upon acidification of flagellar extracts ap- 

 peared to possess no fine structure when viewed in the electron micro- 

 scope but showed up as a spongy, loosely aggregated meshwork, il- 

 lustrated in Fig. 6a. Like actomyosin, however, these precipitates 

 showed a tendency to form filamentous networks. Small changes in 

 pH, and to a much lesser extent decrease in concentration of electro- 

 lytes, resulted in extension of these gels into fine filaments. Some- 

 times, in freshly prepared floes, filament formation was very striking 

 and complete, the dense, opaque, and often rounded gel specimen 

 extending into an anastomosed network of many interwoven, thread- 

 like bridges connecting granular islands. This appearance, which is 

 shown in the optical micrograph in Fig. 6/;, was repeated at the 

 electron microscope level, the ultrastructure again consisting appar- 

 ently of thin filaments of molecular dimensions connecting denser 

 islands of amorphous material (Fig. 6c). Such filamentous forms could 

 be returned partially or completely to the original "globular" state 

 by returning the pH to about 6 or by increasing the electrolyte con- 

 centration. The ability to form filaments diminished as both flagellar 

 and actomyosin precipitates aged until the specimens became inert. 

 That the extended filamentous form might be due to actual molecu- 

 lar rearrangement into fibers seems to be supported by the frequently- 

 observed fact that bundles of filaments were often highly birefringent, 

 the birefringence disappearing as the filaments retracted and reap- 

 pearing as the filaments were extended. 



