What is Dihexa?
Dihexa is better described as a peptidomimetic than as a peptide. The molecular reference for this catalog gives the formula C25H33N3O4 and an average mass of 439.55 and records no residue count, consistent with a structure in which only part of the molecule is standard amino acid. The synonym listed, N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide, shows a tyrosine and isoleucine core capped at one end with a six carbon acyl group and extended at the other by a six carbon amino acid, a design that raises lipophilicity considerably.
In the published literature the angiotensin IV series is studied for interaction with the hepatocyte growth factor and c-Met receptor system. Cell culture work reports that molecules in this series potentiate hepatocyte growth factor dependent c-Met signalling and raise spine density in cultured neurons, and rodent models have probed hippocampal dependent task performance in the animals studied (McCoy, 2013).
What is not settled is substantial. Direct binding to c-Met has been questioned, several reported effects have proven difficult to reproduce independently, and the high lipophilicity complicates in vitro concentration response data because effective free concentration in medium is hard to establish.
Reconstitution & handling
This molecule is markedly more lipophilic than a typical short peptide and does not readily go into plain water at working concentrations. A concentrated stock is commonly prepared in an organic co-solvent such as dimethyl sulfoxide, then diluted into aqueous buffer with the organic fraction kept low enough not to perturb the assay. Concentration remains ordinary arithmetic, labelled mass over total volume.
Storage & stability
Sealed vials are stored at -20 °C, protected from light and moisture, and equilibrated to room temperature before opening. Because the tyrosine phenol is the most reactive group present, prolonged light and oxidising conditions are avoided. Organic stocks are aliquoted, sealed against the moisture uptake dimethyl sulfoxide is notorious for, and protected from repeated freezing and thawing. Aqueous dilutions are prepared fresh.
How it's tested
Each lot is analysed by reversed phase HPLC at 214 and 220 nm, and because a tyrosine is present the profile can also be read at 280 nm as a secondary check. Identity is confirmed by mass spectrometry against the theoretical mass of 439.55 calculated from C25H33N3O4. At this size mass accuracy is a strong identity test, since the acyl and aminohexanoic extensions each shift the mass distinctly.