Fig. 6. NO production by female reproductive tract cells induces S-nitrosylation in human sperm. S-nitrosylated proteins were identified using fluorescently tagged methanethiosulfonate, as described in the text. Negligible levels of labelling were present in controls but treatment with 100 µM spermine NONOate or GSNO caused clear labelling, particularly at the back of the sperm head. Incubation of sperm with primary cultures derived from endometrial or tubal explants (ampulla and isthmus) induced levels of S-nitrosyaltion at least as much as those seen with NONOate.