In vitro decondensation of human sperm chromatin.

The swelling of human sperm head and the decondensation of the sperm chromatin were investigated using a microscopic observation and the increased binding of AMD as the probes. Incubation of the human spermatozoa with 1 mM DTT produced sperm head swelling within 30 min. Addition of soybean trypsin inhibitor or PMSF blocked the swelling induced by 1 mM DTT. The DTT induced a large increase in the binding of AMD to the spermatozoa, to the sperm head and to the triton X-100 treated spermatozoa. This increase in AMD binding was completely abolished by the presence of PMSF. These results suggested the participation of a sulfhydryl reducing agent and a proteolytic enzyme in the sperm head swelling and the chromatin decondensation. The simplicity of probing the chromatin decondensation with AMD binding offers a means to study kinetic and quantitative aspects of the process.