Catalytic Activities of Glycogenin Additional to Autocatalytic Self-glucosylation
| Autor: | William J. Whelan, Miriam D. Alonso, Wieslawa M. Lomako, Joseph Lomako |
|---|---|
| Rok vydání: | 1995 |
| Předmět: |
Uridine Diphosphate Glucose
Glycosylation Glycogenin Molecular Sequence Data Mutant Muscle Proteins macromolecular substances Polymerase Chain Reaction Biochemistry Catalysis law.invention Active center law Complementary DNA Escherichia coli Animals Point Mutation Amino Acid Sequence Cloning Molecular Muscle Skeletal Glycogen synthase Molecular Biology DNA Primers Glycoproteins chemistry.chemical_classification Base Sequence biology fungi Cell Biology Recombinant Proteins carbohydrates (lipids) Kinetics Enzyme chemistry Glucosyltransferases Recombinant DNA biology.protein Tyrosine Phosphorylation Rabbits Oligonucleotide Probes Glycogen |
| Zdroj: | Journal of Biological Chemistry. 270:15315-15319 |
| ISSN: | 0021-9258 |
| Popis: | Glycogenin is the autocatalytic, self-glucosylating protein that initiates glycogen synthesis in muscle and other tissues. We have sequenced the cDNA for rabbit muscle glycogenin and expressed and purified the protein in high yield as well as two mutant proteins in which Phe or Thr replaces Tyr-194, the site of glucosylation. While the wild-type protein can self-glucosylate, the mutants cannot, but all three utilize alternative acceptors by intermolecular glucose transfer for which the mutants have altered specificity. Tyr-194 is therefore not essential for the catalytic activity of glycogenin. All three proteins also hydrolyze UDP-glucose to glucose at rates comparable with the rate of self-glucosylation. The hydrolysis is competitive with glucose transfer to p-nitrophenyl alpha-maltoside. Self-glucosylation, glucosylation of other acceptors, and hydrolysis all appear to be catalyzed by the same active center. In the absence of peptidase inhibitors, the homogenous recombinant proteins of M(r) 37,000 break down to equally active species having M(r) 32,000. The kinetics of self-glucosylation catalyzed by the wild-type enzyme suggest that the reaction could be intermolecular rather than, as previously reported, intramolecular. The wild-type recombinant enzyme and native muscle glycogenin, which is phosphorylated, are inhibited quite differently by ATP at physiological concentration. |
| Databáze: | OpenAIRE |
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