Neutron-Scattering Probe of Complexes of Sodium Dodecyl Sulfate and Serum Albumin during Polyacrylamide Gel Electrophoresis

Guanylyltransferase, an enzyme that catalyzes formation of mRNA 5'-terminal caps, was isolated from HeLa cell nuclei. The partially purified preparation, after incubation with [alpha-32P]GTP, yielded a single radiolabeled polypeptide by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The guanylylated product was stable at neutral and alkaline pHs and had a pI of 4 by isoelectric focusing. An apparent molecular weight of approximately 68,000 was estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. The formation of a covalently linked, radiolabeled GMP-protein complex and the associated release of PPi required the presence of [alpha-32P]GTP and divalent cations and incubation between pH 7 and 9. Reaction with [beta-32P]GTP, [alpha-32P]CTP, [alpha-32P]UTP, or [alpha-32P]ATP did not label the approximately 68,000-dalton polypeptide. Phosphoamide linkage of the GMP-enzyme complex was indicated by its sensitivity to cleavage by acidic hydroxylamine or HCl and not by NaOH or alkaline phosphatase. Both formation of the GMP-enzyme intermediate and synthesis of cap structures of type GpppApG from GTP and ppApG were remarkably temperature independent; the rates of enzyme activity at 0 to 4 degrees C were 30% or more of those obtained at 37 degrees C. Radiolabeled GMP-enzyme complex, isolated by heparin-Sepharose chromatography from reaction mixtures, functioned effectively as a GMP donor for cap synthesis with 5'-diphosphorylated oligo- and polynucleotide acceptors. Alternatively, protein-bound GMP could be transferred to PPi to form GTP. The formation of a guanylylated enzyme intermediate appears to be characteristic of viral and cellular guanylyltransferases that modify eucaryotic mRNA 5' termini.

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Isolation, purification, and characterization of a peptide that contains the β-ketoacyl reductase, enoyl reductase, and β-hydroxyacyl dehydrase activities of the pigeon liver fatty acid synthetase

Canadian Journal of Biochemistry and Cell Biology ◽

10.1139/o85-007 ◽

1985 ◽

Vol 63 (1) ◽

pp. 50-56

Author(s):

Rajinder N. Puri ◽

John W. Porter

Keyword(s):

Fatty Acid ◽

Sodium Dodecyl Sulfate ◽

Gel Electrophoresis ◽

Polyacrylamide Gel Electrophoresis ◽

Sodium Dodecyl ◽

Fatty Acid Synthetase ◽

Polyacrylamide Gel ◽

Liver Fatty Acid ◽

Dodecyl Sulfate ◽

Pigeon Liver

Controlled proteolytic cleavage of pigeon liver fatty acid synthetase with elastase (4% w/w) for 5 h yields two peptides that are designated II and IV. After 5 h of proteolysis the incubation mixture containing these peptides retains all of the component enzyme activities of the fatty acid synthetase complex. The two peptides are then separated by chromatography on an Affi-Gel Blue column. Gel filtration of the fraction containing peptide II yields a homogeneous peptide as shown by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. The molecular weight of this peptide has been estimated to be 130 000 by sodium dodecyl sulfate – polyacrylamide gel electrophoresis, size exclusion chromatography, and amino acid analysis. The sedimentation coefficient for peptide II is approximately 7.4S. Peptide II contains the domains for the β-ketoacyl and enoyl reductases and β-hydroxyacyl dehydrase activities of the fatty acid synthetase complex.

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