Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The sialylation and desialylation in the rat epididiymis is the transference or remotion of sialic acid, to or from an adequate acceptor (glyco or sialogycoprotein). The sialylation of the glycoprotein or glycolipids is determinated by sialyltransferase activity; the homogenates from caput region showed 14 times more sialyltransferase activity than homogenates from cauda epididymis. The desialylation of the sialoglycoproteins is quantified by neuraminidase activity, and it can be observed that the homogenate from the caput zone shows 3 times more activity than homogenates from cauda epididymis. When relatione the activities of sialytransferase/neuraminidase of the caput zone and the cauda zone, the obtained values were 0.19 +/- 0.03 and 0.04 +/- 0.005, respectively. The relation between the activities of neuraminidase/sialiltransferase of the caput and the cauda zone showed the following valves: 5 +/- 0.6 and 25 +/- 3.3, respectively. The results have shown that sialylation is more active in the caput than in the cauda. Besides, while valvating the desialylation we observe that it is more effective in the cauda epididymis.
 ...
PMID:[Role of sialyltransferase and neuraminidase in the epididymis of rats]. 248 56

The cytoplasmic droplet of epididymal spermatozoa is a small localized outpouching of cytoplasm of the tail of unknown significance. EM revealed flattened saccular elements as the near exclusive membranous component of the droplet. Light and electron microscopic immunolabeling for Golgi/TGN markers showed these saccules to be reactive for antibodies to TGN38, protein affinity-purified alpha 2,6 sialyltransferase, and anti-human beta 1,4 galactosyltransferase. The saccules were isolated by subcellular fractionation and antibodies raised against this fraction immunolabeled the saccules of the droplet in situ as well as the Golgi region of somatic epithelial cells lining the epididymis. The isolated droplet fraction was enriched in galactosyltransferase and sialyltransferase activities, and endogenous glycosylation assays identified the modification of several endogenous glycopeptides. EM lectin staining in situ demonstrated galactose and N-acetyl galactosamine constituents in the saccules. Endocytic studies with cationic and anionic ferritin as well as HRP failed to identify the saccules as components of the endocytic apparatus. Epididymal spermatozoa were devoid of markers for the ER as well as the Golgi-associated coatamer protein beta-COP. It is therefore unlikely that the saccular elements of the droplet participate in vesicular protein transport. However, the identification of Golgi/TGN glycosylating activities in the saccules may be related to plasma membrane modifications which occur during epididymal sperm maturation.
 ...
PMID:The cytoplasmic droplet of rat epididymal spermatozoa contains saccular elements with Golgi characteristics. 822 42

Spermatozoa acquire fertilizing ability during passage through the epididymis. Modification of oligosaccharide moieties on sperm surface glycoproteins are some of the biochemical changes believed to be important in the production of functionally mature spermatozoa during passage through the epididymis. In an attempt to understand the mechanism underlying these modifications, we quantified four glycosyltransferase activities (the enzymes that catalyze the transfer of sugar residues from nucleotide sugar donor to the sugar chains on glycoproteins and glycolipids) of spermatozoa and fluid from various regions of the epididymis. Our results are as follows. (1) Only 10-20% of the total glycosyltransferase activities (sialyltransferase, fucosyltransferase, galactosyltransferase, and N-acetyl glucosaminyltransferase) sedimented with the spermatozoa; the remaining 80-90% of the four enzymes were present in soluble form in the epididymal fluid. (2) When the four transferase activities were expressed per 10(6) spermatozoa, only sialyltransferase and fucosyltransferase activities showed maturation-dependent changes. The former enzyme was significantly higher on the proximal caput spermatozoa and the latter on the distal caput spermatozoa. The higher levels of the two enzymes on caput spermatozoa could be due to their binding to the endogenous sugar acceptor molecules on the sperm surface, and subsequent release following sequential sialylation and fucosylation of the molecules in the proximal and distal caput spermatozoa, respectively. (3) When spermatozoa from the proximal and distal caput, corpus, and proximal and distal cauda were incubated with fucose-labeled nucleotide sugar (GDP[14C]fucose), higher levels of radioactivity were routinely incorporated into the spermatozoa from the distal caput. (4) The [14C]fucose-labeled spermatozoa or sperm plasma membranes, when solubilized, resolved on SDS-PAGE, and visualized by autoradiography, showed that the radioactivity had been incorporated into an endogenous acceptor of 86 kDa (major component) and several minor components. Treatment of the solubilized spermatozoa with N-glycanase suggested that the [14C]fucose is mainly present on N-linked oligosaccharide units. These studies demonstrate that some of the sperm surface components are fucosylated during sperm maturation. The potential significance of the in vitro fucosylation of sperm surface components in the production of functionally mature spermatozoa is discussed.
 ...
PMID:Glycosylation of rat sperm plasma membrane during epididymal maturation. 843 31

Sperm surface glycoproteins are modified during passage through the epididymis, a process believed to be important in the production of functionally mature spermatozoa. The effect of various cytokines on reproductive events has recently been investigated, with conflicting results. In the present investigation, the effect of interferon-alpha-2b (IFN alpha 2b) on sialyltransferase (ST) activity and beta-galactoside alpha-2,6-sialyltransferase (Gal 2,6-ST) mRNA expression was studied in rat testicular tissue. The results revealed the presence of Gal 2,6-ST mRNA in rat testicular tissue, similar in molecular size to that found previously in rat spleen, lung, ovary, kidney, heart, and brain. In addition, we observed that IFN alpha 2b reduced Gal 2,6-ST mRNA and ST activity in rat testes by a comparable magnitude. These findings provide insight into an additional mechanism by which cytokines may affect the reproductive system.
 ...
PMID:Interferon alpha-2b modulates beta-galactoside alpha-2,6-sialyltransferase gene expression in rat testes. 856 5