Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.6 (sialyltransferase)
 1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Some properties of the sialyltransferase activity of homogenates prepared from normal human platelets were investigated using asialo-fetuin as substrate. The enzyme activity was optimal at pH 6.5 and was stimulated by divalent cations in the order Mg2+ greater than Mn2+ greater than Ca2+. Buffers of high ionic strength strongly reduced the activity. ATP and ADP were not inhibitors at 0.1 mM concentration, but AMP, CTP and CMP reduced the activity by 15-30%. A native endogenous acceptor for the enzyme activity was located in the platelet homogenates. The range of fetuin-sialyltransferase activity found in platelets isolated from 6 normal donors was 79 +/- 39 pmol/h/mg protein (mean +/- SD). The platelets of patients with Glanzmann's thrombasthenia and the Bernard-Soulier syndrome, which are characterized by different membrane glycoprotein deficiencies, were shown to have fetuin-sialyltransferase activities within the normal range indicating that the membrane glycoprotein defects in the platelets of these patients are not associated with the absence of sialyltransferase activity.
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PMID:Glycoprotein-sialyltransferase activity of normal human, thrombasthenic and Bernard-Soulier platelets. 616 43

The translocation of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) across rat liver Golgi-derived vesicles has been studied. Vesicles of the same topographical orientation as in vivo were incubated with a mixture of [adenine-8-3H]PAPS and [35S]PAPS. The tritium to radiolabeled sulfur ratio of the incubation medium was 1.73 +/- 0.03 while that in the vesicles was 1.82 +/- 0.13. This strongly suggests that the entire PAPS molecule was being translocated across the Golgi vesicle membrane even though intact PAPS could not be detected within the vesicles. Translocation of PAPS resulted in accumulation of solutes within vesicles. This accumulation was temperature dependent, saturable (apparent Km = 0.7 microM; Vmax = 25 pmol/mg of protein/10 min), and inhibited by the substrate analogue 3',5'-ADP but not by 2',5'-ADP. Translocation of PAPS was inhibited following treatment of Golgi vesicles with Pronase under conditions in which the activity of a lumenal Golgi membrane marker such as sialyltransferase was not. This result is consistent with the existence of a PAPS carrier protein, portions of which face the cytoplasmic side of the Golgi membrane.
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PMID:Translocation of adenosine 3'-phosphate 5'-phosphosulfate into rat liver Golgi vesicles. 670 70

ADP-ribosylation factors (Arf), a family of small GTP-binding proteins, play important roles in intracellular trafficking in animal and yeast cells. Here, we investigated the roles of two Arf homologs, Arf1 and Arf3 of Arabidopsis, in intracellular trafficking in plant cells. We generated dominant negative mutant forms of Arf 1 and Arf3 and examined their effect on trafficking of reporter proteins in protoplasts. Arf1[T31N] inhibited trafficking of H(+)-ATPase:green fluorescent protein (GFP) and sialyltransferase (ST):GFP to the plasma membrane and the Golgi apparatus. In addition, Arf1[T31N] caused relocalization of the Golgi reporter protein ST:GFP to the endoplasmic reticulum (ER). In protoplasts expressing Arf1[T31N], ST:red fluorescent protein remained in the ER, whereas H(+)-ATPase:GFP was mistargeted to another organelle. Also, expression of Arf1[T31N] in protoplasts resulted in profound changes in the morphology of the ER. The treatment of protoplasts with brefeldin A had exactly the same effect as Arf1[T31N] on various intracellular trafficking pathways. In contrast, Arf3[T31N] did not affect trafficking of any of these reporter proteins. Inhibition experiments using mutants with various domains swapped between Arf1 and Arf3 revealed that the N-terminal domain is interchangeable for trafficking inhibition. However, in addition to the T31N mutation, motifs in domains II, III, and IV of Arf1 were necessary for inhibition of trafficking of H(+)-ATPase:GFP. Together, these results strongly suggest that Arf1 plays a role in the intracellular trafficking of cargo proteins in Arabidopsis, and that Arf1 functions through a brefeldin A-sensitive factor.
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PMID:ADP-ribosylation factor 1 of Arabidopsis plays a critical role in intracellular trafficking and maintenance of endoplasmic reticulum morphology in Arabidopsis. 1217 64