Mechanochemical coupling in flagella: I. Movement-dependent dephosphorylation of ATP by glycerinated spermatozoa

The ATP-reactivated movement of the tails of glycerinated sea urchin spermatozoa is prevented when the spermatozoa are broken by vigorously mixing the sperm suspension. Broken spermatozoa dephosphorylate ATP at a lower rate than unbroken spermatozoa, and this difference may represent movement-coupled dephosphorylation of ATP by the motile spermatozoa. This conclusion is supported by experiments which show that the difference in ATP dephosphorylation between unbroken and broken sperm suspensions is specifically inhibited by thiourea or by increased viscosity, which inhibit motility without inhibiting the dephosphorylation of ATP by the broken sperm suspensions. The movement-dependent dephosphorylation of ATP appears to be proportional to the beat frequency of the spermatozoa, and not, as in the case of muscle, to their energy expenditure. If the movement-dependent dephosphorylation of ATP is related to the estimated number of motile spermatozoa in the suspension, the number of ATP molecules used per beat by each molecule of the flagellar ATPase, dynein, lies between 0.3 and 2.5.