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 composition of tissue gangliosides is thought to result mainly from the active regulation and selective expression of specific enzymes responsible for their metabolism. In the last few years, we have purified several rat brain sialyltransferases to homogeneity; the availability of these highly purified enzymes enabled us to investigate their regulation and expression at the molecular level. Thus, we studied the regulation of sialyltransferase activities, in particular, CMP-NeuAc:GM1 and CMP-NeuAc:LacCer sialyltransferases by a phosphorylation/dephosphorylation mechanism. Protein kinase C was added to a standard enzyme assay mixture containing [gamma-32P]ATP, and the activity of the enzyme was measured after various incubation times. We found that treatment of several sialyltransferases by protein kinase C decreased their activities in a time-dependent manner. Analyses of 32P-labeled amino acids revealed that the major phosphorylation site of CMP-NeuAc:GM1 alpha 2-->3 sialyltransferase (ST-IV) was serine and that for CMP-NeuAc:LacCer alpha 2-->3 sialyltransferase (ST-I) was primarily threonine. Partial recovery of the enzyme activity could be achieved by treatment of the phosphorylated sialyltransferases with rat brain protein phosphatase. We conclude that the activities of sialyltransferases can be modulated by protein kinase C and protein phosphatase and this may represent a potential regulatory mechanism for ganglioside biosynthesis.
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PMID:Regulation of sialyltransferase activities by phosphorylation and dephosphorylation. 772 15

CMP-NeuAc:GM1 alpha 2,3-sialyltransferase (ST-IV) was purified to homogeneity from rat brain. Microsequencing of the tryptic peptides derived from the purified enzyme revealed two amino acid sequences homologous to the 14-3-3 proteins. A polyclonal antibody was raised against purified ST-IV. A 33 kDa protein was co-immunoprecipitated from rat brain extracts with the anti-(ST-IV) antibody as detected by Western blot analysis. This protein was identified as a subtype of 14-3-3 family by an anti-(14-3-3) antibody. Screening of a rat brain lambda gt11 library using the anti-(ST-IV) antibody resulted in the identification of a cDNA clone coding for the subtype of 14-3-3 protein. These results indicate an association of the 14-3-3 protein with the sialyltransferase. Since the 14-3-3 protein has PKC inhibitor activities and the activity of sialyltransferases is, at least in part, regulated by PKC, the association of the 14-3-3 protein with ST-IV may indicate a role for this protein in the post-translational regulation of the sialyltransferase activity through the processes of phosphorylation and dephosphorylation.
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PMID:Association of a 14-3-3 protein with CMP-NeuAc:GM1 alpha 2,3-sialyltransferase. 869 95