Isolation and characterization of a semen-specific protein from human seminal plasma: a potential new marker for semen identification.

The identification of semen is of paramount importance in the investigation of rape and other crimes involving sexual assault. The most commonly used procedures for semen identification center on the detection of sperm o r the detection of prostatic acid phosphatase activity; methods involving the detection of spermine, choline, or semen antigens are less commonly employed. Unfortunately, none of these procedures is without one or more significant problems. For example, sperm will not be found in the semen of vasectomized or aspermic males; moreover, sperm are mechanically labile and their unequivocal identification in suspected semen stains is often difficult. Also, sperm are cleared from the vagina fairly rapidly and hence may not be found in posteoital vaginal washings. Thus the failure to detect sperm in suspect material by no means counterindicates semen. In the case of the acid phosphatase test, the problems are different. Acid phosphatase is not at all unique to semen or prostatic tissue; this enzyme activity is ubiquitous in nature. Moreover, there is evidence that prostatic acid phosphatase and the acid phosphatase found in normal vaginal secretions are genetically identical and that both are genetically identical to lysosomat acid phosphatase found in most tissues; 2 therefore, the genetic basis of specificity of the acid phosphatase test is in question. The quantitative test can only be based on the extraordinarily high level of acid phosphatase activity in semen; the low levels of activity often found in postcoital vaginal washings are thus equivocal with respect to the question of semen detection. The other tests for semen identification are similarly suspect in reference to their specificity. From the foregoing it is apparent that it would be desirable to have alternative tests for the detection of semen. A good alternative test should meet several criteria. It should be based on the detection of a semen marker for which the biological basis of specificity could be demonstrated; this condition virtually dictates that the marker should be a protein since protein synthesis is under direct genetic control. To avoid the problem posed by vasectomized and aspermic males, the marker should be a component of seminal plasma. A good marker should be stable in stains and in the vaginal environment. Finally,