Oxidation of methionine residues in equine growth hormone by Chloramine-T.

This research paper studies how methionine residues in the equine growth hormone react to Chloramine-T, and finds that their oxidation doesn’t alter the protein’s structure or its capability to bind to specific receptors. The most reactive methionine was found to be the fourth one, with the 123rd being the least reactive.

Reacting Methionine Residues with Chloramine-T

• This research is centered around the reaction of methionine residues in the equine growth hormone with Chloramine-T, a reagent commonly used in organic synthesis.
• The scientists used a 20.0-fold molar excess of Chloramine-T over methionine for full oxidation of the four residues of the protein. This means for each mole of methionine, 20 moles of Chloramine-T were used to ensure complete oxidation of all methionine residues in the equine growth hormone.

Rate of Methionine Reaction

• Of the four methionine residues present in the growth hormone, the research found that the fourth residue was the most reactive. This means that it was quickest to undergo oxidation when Chloramine-T was added.
• The order of reactivity was Methionine 4 > Methionine 72 > Methionine 178 > Methionine 123, with Methionine 123 being the least reactive residue.

Impact on Protein Structure and Function

• Despite the oxidation of all four methionine residues, the structure of the protein remained unchanged. This was confirmed through the use of circular dichroism spectra, a technique used to determine the secondary structure of proteins.
• In addition to the structure, the binding capacity or ability of the protein to bind to specific receptors also remained intact even after the complete oxidation. Binding assays, experimental procedures used to measure the interaction between two molecules, were used to confirm this.

Comparison with Bovine Growth Hormone

• The findings of this research corroborated data previously obtained with studies on the bovine growth hormone.
• This suggests a level of consistency across different species’ growth hormones when it comes to the reactivity of methionine residues and the influence of their oxidation on protein structure and function.