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Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase01:27

Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase

Phase II biotransformation reactions are essential for detoxifying and eliminating xenobiotics, including many pharmaceutical compounds. These reactions typically involve conjugation, the covalent attachment of polar endogenous groups such as glucuronic acid, sulfate, methyl, or acetyl moieties to functional groups introduced during Phase I metabolism. The resulting conjugates are more water-soluble, enabling efficient renal or biliary excretion.The major classes of Phase II enzymes include...
Allosteric Proteins-ATCase01:19

Allosteric Proteins-ATCase

Binding sites linkages can regulate a protein's function.  For example, enzyme activity is often regulated through a feedback mechanism where the end product of the biochemical process serves as an inhibitor.
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Biosynthesis of Nucleic Acids01:28

Biosynthesis of Nucleic Acids

Nucleic acid biosynthesis is a fundamental biochemical process that produces the purine and pyrimidine nucleotides essential for DNA and RNA synthesis. This pathway maintains a balanced nucleotide pool, preventing imbalances that could jeopardize genetic integrity and cellular function. Given the crucial role of nucleotides, their synthesis is tightly regulated to ensure proper cellular homeostasis.Purine BiosynthesisThe biosynthesis of purine nucleotides begins with ribose-5-phosphate, a...
Covalently Linked Protein Regulators02:04

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
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Nonsense-mediated mRNA Decay02:27

Nonsense-mediated mRNA Decay

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Quantitative Methods to Study Protein Arginine Methyltransferase 1-9 Activity in Cells
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Quantitative Methods to Study Protein Arginine Methyltransferase 1-9 Activity in Cells

Published on: August 7, 2021

Putrescine N-methyltransferases--a structure-function analysis.

Michael Teuber1, Mohammad E Azemi, Foroogh Namjoyan

  • 1Institute of Pharmacy, Faculty of Science I, Martin-Luther University Halle-Wittenberg, Halle, Saale, Germany.

Plant Molecular Biology
|January 16, 2007
PubMed
Summary

Putrescine N-methyltransferase (PMT) enzymes, crucial for plant alkaloids, differ significantly from spermidine synthases (SPDS). Mutating PMT active sites unexpectedly abolished its function, revealing distinct substrate binding.

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Efficient Purification and LC-MS/MS-based Assay Development for Ten-Eleven Translocation-2 5-Methylcytosine Dioxygenase
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Efficient Purification and LC-MS/MS-based Assay Development for Ten-Eleven Translocation-2 5-Methylcytosine Dioxygenase

Published on: October 15, 2018

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Quantitative Methods to Study Protein Arginine Methyltransferase 1-9 Activity in Cells
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Efficient Purification and LC-MS/MS-based Assay Development for Ten-Eleven Translocation-2 5-Methylcytosine Dioxygenase
10:33

Efficient Purification and LC-MS/MS-based Assay Development for Ten-Eleven Translocation-2 5-Methylcytosine Dioxygenase

Published on: October 15, 2018

Area of Science:

  • Plant biochemistry
  • Enzymology
  • Molecular evolution

Background:

  • Putrescine N-methyltransferase (PMT) initiates the biosynthesis of vital plant compounds like nicotine and tropane alkaloids.
  • PMT is hypothesized to have evolved from spermidine synthases (SPDS), enzymes involved in general polyamine metabolism.

Purpose of the Study:

  • To elucidate the key differences between PMT and SPDS enzyme families.
  • To investigate the evolutionary relationship and functional divergence of PMT and SPDS.

Main Methods:

  • Cloning of eight new PMT cDNA sequences from Solanaceae and Convolvulaceae species.
  • Heterologous expression and catalytic activity assays of cloned PMT enzymes.
  • Site-directed mutagenesis of PMT active site residues based on SPDS structural data.
  • Comparative protein modeling of PMT using SPDS crystal structures.

Main Results:

  • Newly identified PMT polypeptides showed high sequence identity (76–97%) and conserved amino acid differences compared to SPDS.
  • All expressed enzymes exhibited exclusive PMT catalytic activity with K(cat) values ranging from 0.16 to 0.39 s⁻¹.
  • Mutagenesis of PMT active site residues critical for SPDS function resulted in a complete loss of PMT activity.
  • Protein modeling indicated conserved overall folds but differential binding of substrates and cosubstrates (S-adenosylmethionine, decarboxylated S-adenosylmethionine, putrescine) between PMT and SPDS.

Conclusions:

  • PMT and SPDS represent distinct enzyme families with specialized active sites, despite conserved protein folds.
  • The observed differences in substrate and cosubstrate binding are crucial for the distinct functions of PMT and SPDS.
  • Evolutionary modifications in the active site likely led to the functional specialization of PMT from an SPDS ancestor.