Fluorescein mercuric acetate as a dye for fluorescence and electron microscope detection of -SH groups in mouse sperm protamines: a critical evaluation.

Fluorescein Mercuric Acetate (FMA), a specific fluorescent dye for thiols, was tested as a possible reagent for the ultrastructural detection of -SH groups in sperm chromatin protamines. It was shown that FMA may be profitably used for staining at electron microscopy the chromatin -SH groups of caput epididymidis spermatozoa. Like other mercury compounds, FMA proved to be unstable under the electron beam; therefore the use of low beam intensity, and cooling of the specimens are recommended. The main advantages of this staining method are the relatively lower toxicity of FMA, compared to other organic mercurials, and the opportunity to compare the fluorescence patterns on semithin sections with the corresponding ultrastructural findings on thin sections.