Purification and localization of a calcium-binding protein in human spermatozoa

The purpose of this study was to purify a calcium-binding protein (CalBP) from human spermatozoa of 226 men and to determine the localization of this protein in spermatozoa. The sperm cells were extracted with 0.6 M KCl, and the KCl extract was then subjected to gel filtration and high performance liquid chromatography. Two CalBPs of Mr = 38 kDa and 52 kDa were found by 45Ca(2+)-binding on blotted proteins. Only a 52 kDa CalBP (CalBP-52) was purified to a final yield of 0.007%. The isoelectric point of this protein was 5.1. The human CalBP-52 reacted with rabbit antiserum directed against rat 52 kDa CalBP. An immunocytochemical study showed that this protein was localized on the sperm head. It is postulated that this protein may have important functions related to Ca(2+)-transport into sperm cells.