Octet Biomolecular binding kinetics

octet-biomolecular-binding-kinetics-application-note-4014-en-1—data.pdf

kobs is the observed rate constant. At the same time AB complex is forming, it also decays back to A and B. The term kobs reflects the overall rate of the combined association and dissociation of the two binding partners.

octet-biomolecular-binding-kinetics-application-note-4014-en-1—data, page 8

• This PDF uses observed rate constant rather than ka as done by a sample calculation of SPR (another pdf)

• Solve this equation to get $k_{obs}$ = the equation is specific to association
• A single $k_{obs}$ value would be collected for each analyte concentration
• The paper quotes that “A is the asymptote of the binding curve”

Comparing this equation to Pasted image 20250424154424.png from SPR-Pages - Data fitting methods, the following conclusions can be made:

1. $k_{obs}=k_a\ast \text{(Analyte Concentration)}+k_d$
2. t can be scaled to account for time taken for the association phase to start (time measurement may have started pre-emptively, only producing a baseline signal)
3. A is simply R_eq, the new baseline that is achieved after the association phase has finished
   • Similar to K_m, this can either be fitted or it can be experimentally observed

• Solve this equation to get $k_d$ = the equation is specific to dissociation
• A is the same R_eq asymptote prior to the start of the dissociation phase
• This would be globally fit across different analyte concentrations, because $k_d$ is inherently constant for different analyte concentrations

• Use this equation to solve for $k_a$
• With varying $k_{obs}$, varying analyte concentrations, and single $k_d$ estimate, $k_a$ can be calculated
• This is derived form the relationship: $k_{obs}=k_a\times C+k_d$

• Use this equation to solve for $K_D$