why is the sequence written four different ways across four vendor sites
Same nominal compound, four suppliers, four different sequence representations. One uses three-letter codes, one uses single-letter, one has a different N-terminal modification listed, and one just gives a molecular formula that does not match the other three.
At least two of those four cannot be selling the same thing. Possibly all four are selling something slightly different and none of them are lying, because the naming convention in this corner of the catalogue is genuinely a mess.
My process now: get the sequence in writing before ordering, compute the theoretical monoisotopic mass, and check it against whatever the COA claims. It takes five minutes and it has stopped me ordering twice.
best — the order this archive was captured in
The mess is partly historical and partly convenient. TB-500 and Thymosin Beta-4 get used interchangeably and they are not the same product — one is a fragment, one is the full protein, and the price difference tells you which one anybody is actually shipping.
Vendors know this. Some of them are propagating an industry-wide confusion rather than inventing one, which is a mitigation and not an excuse.
this is the specific case that made me start checking. i ordered the full protein price and got fragment documentation, and when i asked, the answer was "same thing" delivered with total confidence.
and the correct response to "same thing" is "then send me the sequence and the theoretical mass". it ends the conversation one way or the other.
and if they send a mass that does not match the sequence they sent, you have learned something enormous for the price of one email.
WXT sent me the sequence and the theoretical mass unprompted. once, ever, unprompted. it is a very short list.
same list as the water-content one, which is not a coincidence.
BPC is the other bad case. the sequence gets written at least three ways and the acetate versus free-acid distinction is regularly dropped entirely.
Adding "get the sequence in writing" to the c/researchpeptides rules as a suggested practice rather than a requirement. It is the highest-value five minutes available in this community.
the GH secretagogue catalogue has been like this for thirty years. edit: and the naming chaos there was load-bearing for a lot of very confident marketing.
how do you compute the theoretical mass? is there a tool or is this a spreadsheet situation
plenty of free calculators, and for a short peptide a spreadsheet of residue masses plus water works fine. it is addition.
- 1The mess is partly historical and partly convenient. TB-500 and Thymosin…6 comments in this branch · started by u/analog_alphabet