Serine phosphorylation of flagellar proteins associated with the motility activation of hamster spermatozoa

It has been widely accepted that the motility of spermatozoa is regulated b y phosphorylation of flagellar proteins. In order to understand the regulat ory mechanisms of the motility of mammalian spermatozoa, we investigated pr otein phosphorylation associated with motility activation. For precise anal yses, we designated four steps in motility activation. They were pre-initia tion (immotile spermatozoa), initiation (calcium-independent activation), a ctivation (calcium-dependent activation), and hyperactivation. We detected 66K, 58K, and 36K proteins as the phosphoproteins related to the motility o f spermatozoa. Among them, 36K proteins were separated into two different i soelectric proteins. When the motility of the spermatozoa was changed from pre-initiation to initiation, which is independent of calcium, 66K and 58K proteins were exclusively phosphorylated. When the spermatozoa were activat ed from the initiation by extracellular calcium, two types of 36K proteins were phosphorylated. All these proteins were phosphorylated at the serine r esidues. On the basis of the present results, we propose that the motility of hamster spermatozoa may be regulated through at least two pathways of pr otein phosphorylation. Proteins of 66K and 58K are involved in a calcium-in dependent path way to initiate the motility of spermatozoa. On the other ha nd, two types of 36K proteins are involved in a calcium-dependent pathway t o activate the motile spermatozoa.