Low molecular weight proteins in human seminal plasma electrophoretical evidence of their vesicular origin

The protein composition of seminal plasma (SP), two-fractions split ejaculates and expressed prostatic secretions (EPS) from healthy and fertile donors or from infertile patients has been analyzed under proteolysis-blocking and denaturing conditions by 5-20% gradient SDS-PAGE. EPS protein patterns were found to be strikingly similar, both in protein types and concentrations. The same was true for the SP samples. Co-electrophoresis and comparison of the patterns obtained allowed to identify a medium-sized protein (MW 75-80,000 daltons) and low-MW proteins (MW 10-25,000 daltons) as of vesicular origin. Furthermore, prostatic and vesicular proteins were found to migrate into different zones of the gels, giving raise to an unexpected MW "complementarity". A similar finding was obtained by comparing the protein spectra of fluid from vesicular massage (EVS), EPS and SP from a man with moderate asthenozoospermia. However, analysis of nine other EVS samples by the same electrophoretical technique revealed that the majority of them were (sometimes heavily) contaminated by prostatic proteins. It was concluded that SDS-PAGE on gradient gels is of help to distinguish and characterize the proteins secreted by the two major male accessory glands. Such a finding has both research and clinical applications.