Contractile Proteins of Marine Invertebrate Spermatozoa

Starfish sperm flagella prepared by ultrasonic disruption were extracted with digitonin and 0.6 M KI.2. Flactin, a flagellar protein analogous to muscle actin, was obtained which undergoes viscosity changes similar to depolymerization and polymerization. Like actin, flactin does not hydrolyze ATP.3. Flactospermosin, however, like actomyosin, does split ATP, and also precipitates when diluted 5-10-fold with deionized water. If ATP is present, superprecipitation occurs. In 0.6 M KC1 solutions of flactospermosin, ATP causes a rapid drop in viscosity, which reverts to the initial value as the ATP becomes hydrolyzed.4. The intrinsic viscosity, reduced viscosity extrapolated to infinite protein dilution, of flactin has a value of about 0.2, indicating that this is a fairly asymmetric molecule.5. While spermatozoa appear to possess the potential for employing a dual protein complex in flagellar wave production, this does not imply that, on a fine structural level, a sliding filament mechanism underlies flagellar movement. Upon interaction of the flactin and the spermosin, ATP hydrolysis could induce the necessary configurational change.