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)

We have used Chinese hamster ovary (CHO) cells and a murine lymphoma cell line to study the recycling of the 215-kD and the 46-kD mannose 6-phosphate receptors to various regions of the Golgi to determine the site where the receptors first encounter newly synthesized lysosomal enzymes. For assessing return to the trans-most Golgi compartments containing sialyltransferase (trans-cisternae and trans-Golgi network), the oligosaccharides of receptor molecules on the cell surface were labeled with [3H]galactose at 4 degrees C. Upon warming to 37 degrees C, the [3H]galactose residues on both receptors were substituted with sialic acid with a t1/2 approximately 3 hrs. Other glycoproteins acquired sialic acid at least 8-10 times slower. Return of the receptors to the trans-Golgi cisternae containing galactosyltransferase could not be detected. Return to the cis/middle Golgi cisternae containing alpha-mannosidase I was measured by adding deoxymannojirimycin, a mannosidase I inhibitor, during the initial posttranslational passage of [3H]mannose-labeled glycoproteins through the Golgi, thereby preserving oligosaccharides which would be substrates for alpha-mannosidase I. After removal of the inhibitor, return to the early Golgi with subsequent passage through the Golgi complex was measured by determining the conversion of the oligosaccharides from high mannose to complex-type units. This conversion was very slow for the receptors and other glycoproteins (t1/2 approximately 20 h). Exposure of the receptors and other glycoproteins to the dMM-sensitive alpha-mannosidase without movement through the Golgi apparatus was determined by measuring the loss of mannose residues from these proteins. This loss was also slow. These results indicate that both Man-6-P receptors routinely return to the Golgi compartment which contains sialyltransferase and recycle through other regions of the Golgi region less frequently. We infer that the trans-Golgi network is the major site for lysosomal enzyme sorting in CHO and murine lymphoma cells.
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PMID:Intracellular movement of two mannose 6-phosphate receptors: return to the Golgi apparatus. 296 50

The recycling of plasma membrane glycoproteins to the Golgi complex is well established, but it is not clear which Golgi subcompartments receive this traffic. To date, recycling into the trans-Golgi compartment that contains sialyltransferase and the early Golgi region that contains alpha-mannosidase I has been demonstrated. However, transport into other Golgi compartments has not been reported. In this study we tested the return of cell surface glycoproteins to the Golgi galactosyltransferase compartment using the ldlD mutant of Chinese hamster ovary cells. The cation-independent mannose 6-phosphate/insulin-like growth factor-II receptor recycled through this Golgi region with a half-time of 4 h and was transported to the sialyltransferase compartment as well. Because galactosyltransferase and sialyltransferases are probably located in different trans-Golgi regions in Chinese hamster ovary cells, these results suggest that the two compartments each receive recycling traffic or that recycling glycoproteins enter one region and are then transported to the other. The extent of cell surface protein recycling through the galactosyltransferase compartment was also studied. At least 10 different glycoproteins were transported from the cell surface to this Golgi region. Moreover, our results suggest that recycling glycoproteins make up 12-25% of the flux of cell surface glycoproteins through the Golgi galactosyltransferase compartment; the balance is comprised of newly made glycoproteins.
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PMID:Glycoprotein recycling to the galactosyltransferase compartment of the Golgi complex. 848 26