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1 September 2000 Biosynthesis, Processing, and Subcellular Localization of Rat Spermβ-d-Galactosidase
Catherine A. Chayko, Marie-Claire Orgebin-Crist, Marjorie D. Skudlarek, Daulat R. P. Tulsiani
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Abstract

During spermatogenesis, spermatids synthesize constituent proteins present in mature spermatozoa; however, little information exists on the molecular processes involved. In previous studies, this laboratory reported the characterization of rat sperm β-d-galactosidase. In this paper, we report the localization of this enzyme along with its biosynthesis and processing. An antibody against rat luminal fluid β-d-galactosidase was used to immunolocalize the enzyme in the testis and in epididymal spermatozoa. We found that β-d-galactosidase is localized within the acrosomal cap of spermatids and in the acrosome and cytoplasmic droplet of epididymal spermatozoa. A combination of germ cell radiolabeling, immunoprecipitation, SDS-PAGE, and autoradiography revealed that spermatids produce two forms of β-d-galactosidase, 90 and 88 kDa. During pulse-chase analysis, a 56-kDa form appeared. Treatment of β-d-galactosidase immunoprecipitates from testicular spermatozoa with N-glycanase or Endo H revealed that both the 90- and 88-kDa forms become a 70-kDa polypeptide on SDS-PAGE. Since Endo H or N-glycanase treatment provided similar results, the presence of extensive N-linked high mannose/hybrid-type glycans on these proteins is indicated. Treatment of the 56-kDa form of β-d-galactosidase with Endo H or N-glycanase resulted in the appearance of 52- and 50-kDa forms, respectively. This result suggests that the 56-kDa form contains N-linked high mannose/hybrid as well as complex oligosaccharides. During epididymal maturation, the 90-kDa form of β-d-galactosidase persists in caput epididymal spermatozoa and is gradually converted to a major 74-kDa form in cauda spermatozoa. In addition to the 90- to 74-kDa forms, cauda spermatozoa show a 56- to 52-kDa form on Western immunoblots. Since only the high-molecular weight forms of β-d-galactosidase are present on immunoblots of isolated sperm heads, we suggest that they are acrosomal in origin and that the 56-kDa form, which is processed to 52 kDa in cauda spermatozoa, is associated with the cytoplasmic droplet.

Catherine A. Chayko, Marie-Claire Orgebin-Crist, Marjorie D. Skudlarek, and Daulat R. P. Tulsiani "Biosynthesis, Processing, and Subcellular Localization of Rat Spermβ-d-Galactosidase," Biology of Reproduction 63(3), 688-696, (1 September 2000). https://doi.org/10.1095/biolreprod63.3.688
Received: 7 October 1999; Accepted: 1 April 2000; Published: 1 September 2000
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KEYWORDS
epididymis
sperm
sperm maturation
spermatid
spermatogenesis
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