Solving The Mystery Of What Puts Sperm 'In The Mood'

Mark Platt and colleagues note in the new study that sperm cannot fertilize an egg immediately after entering the female reproductive tract. Sperm must acquire this ability after undergoing an activation process called "capacitation." Scientists have known for years that this process involves phosphorylation. That common biological modification causes cellular activities to be turned "on" by the addition of phosphate molecules to certain amino acids within proteins. However, the specific biochemical details have been a deep mystery.

Using laboratory mice, the researchers compared the extent of phosphorylation in both capacitated and noncapacitated sperm samples. They identified 44 peptides exhibiting differential phosphorylation, on 59 specific amino acids, suggesting that modification of these particular sites is essential for the capacitation process. The relative ratio of phosphorylation between the capacitated and noncapacitated samples were also reported, providing the first biochemical description of what puts sperm "in the mood."