Presence of soluble b-type cytochrome in human seminal fluid

In 1951 it was shown that human spermatozoa contained cytochromes a, b, and c. It was noted that the cytochromes were confined to the sperm and were not found in seminal fluid. More recently we have observed in seminal plasma a soluble component that has a typical spectrum of a reduced cytochrome b, but can be distinguished from the b-type cytochromes in other mammalian tissue. This substance, seminal plasma cytochrome (SPC) has not been described before. The spectrum of reduced SPC has peaks of 4290 A and 5620 A. The reduction can be induced chemically with sodium dithionite or enzymatically using reduced nicotinamide adenine dinucleotide as electron donor. The reduced SPC can bind carbon monoxide, giving an absorption peak in the range of 4140 A to 4250 A. SPC was present in semen from vasectomized men and infertility patients with azoospermia, as well as in the seminal plasma of normal donors. This indicates that the enzyme is not present as an artifact caused by leakage from spermatozoa. The possible function of SPC in seminal plasma is unknown at the present time.