Very strong binding can be difficult to measure directly. An experimental competitor can make the measurement informative, provided its contribution is accounted for. Primary study
What was reported
The investigators used isothermal titration calorimetry with glycine as a weaker competing ligand to study copper binding by GHK and DAHK. They reported predominantly one-to-one binding and conditional dissociation constants after correcting for competitor and buffer effects at a specified pH. The energetic contributions to binding differed between the two peptides. Primary report
Our appraisal: an affinity value needs its definition
A conditional binding constant is not a context-free label attached permanently to a molecule. The value is defined for particular chemical conditions and assumptions. Comparing values from different reports requires checking that those definitions are compatible.
The observed heat in a titration may contain more than the desired binding event. Proton transfer and interactions with competing ligands or buffer can contribute. Correcting for those processes is part of extracting the quantity of interest, not merely a cosmetic adjustment to a result.
Strong equilibrium binding also differs from slow exchange. Affinity describes an equilibrium relationship; exchange kinetics describe how quickly the system changes. One cannot be inferred solely from the other.
The comparison between GHK and DAHK is molecularly specific. It does not provide a measured affinity for another peptide whose sequence was not tested, even if a product description groups them all as copper peptides.
This paper supports careful analytical characterization. It does not establish human bioavailability, selective delivery, clinical benefit, or the composition of a supplier's vial. Those claims require additional evidence that asks the relevant question rather than reusing a binding constant as a general quality or efficacy score.
Frequently asked questions
Was calorimetry used?
Yes.
Why was glycine included?
As a weaker competing ligand in the measurement.
Were buffer contributions considered?
Yes.
Are conditional constants independent of chemical conditions?
No.
Is equilibrium affinity identical to exchange speed?
No.
Does this measure another untested copper peptide's affinity?
No.
Does strong binding prove clinical benefit?
No.