Additional experiments suggested that, NO aside, nothing else in the sperm seems able to activate the eggs. To prove this, the scientists turned to oxyhemoglobin, the familiar oxygen transporter in blood. This protein mops up and "neutralizes" all NO in its vicinity before the gas can perform any other function. And Epel's team found that when they injected oxyhemoglobin into the eggs, the sperm could no longer activate them and the calcium levels in their cytoplasms remained low; nothing replaced the function of NO.
It will take more study to determine if NO really is the crucial factor in switching an egg on, but if it is, it might explain some cases of male infertility: if a man's sperm doesn't produce enough NO, it may be unable to successfully fertilize an egg. The good news is that it is probably not a problem that can't be fixed. A little extra NO, introduced to the egg during in vitro fertilization (IVF,) might just do the trick, giving some couples the chance to have children of their own.