The abundant 19‐kilodalton protein associated with human sperm nuclei that is related to seminal plasma α‐inhibins

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Abstract
A basic protein with a relative molecular mass of 19 kDa has been identified and isolated to purity from sonication‐resistant, partially demembranized human sperm nuclei. Several criteria prove that this is the unique sperm‐specific protein, which was previously thought to be a sperm/testis histone. Partial primary structure sequencing demonstrates homologies with human seminal α‐inhibins and semenogelin. From the sequence and Western‐blotting data with antibodies against basic seminal inhibin‐like peptide, we propose that this 19‐kD protein is a product of 52‐kDa semenogelin processing. The 19‐kDa protein was not found among seminal plasma proteins and may be protected from further cleavage into inhibin‐like peptides by its association with the sperm head Immunofluorescence data indicate its localization in the nuclear periphery, with preferential concentration at the acrosome calyx boundary.