[Nescafe]

Hi,

Okay, sooo I always get super confused with the terms in the subject what they mean, how they are different, when to use each and how they are calculated. For instance Ka vs Kobserved or when to use Ki vs IC50 or what formulas are used to calculate them. I'm so fraustrated that it's affecting my sleep so help a brother out please.

Nescafé.

[Babcock_Hall]

What do you mean by Ka?  This paper might be a good starting point.

Biochem Pharmacol. 1973 Dec 1;22(23):3099-108.
Relationship between the inhibition constant (K1) and the concentration of inhibitor which causes 50 per cent inhibition (I50) of an enzymatic reaction.
Cheng Y, Prusoff WH.

[Babcock_Hall]

Here is another reference on IC50 that a friend of mine turned up:  Curr Top Med Chem. 2012 Jun 1;12(11):1282-90.  Caldwell GW, Yan Z, Lang W, Masucci JA.  "The IC50 Concept Revisited."

And one more:  Biochem Med Metab Biol. 1987 Jun;37(3):344-9.
Calculation of inhibitor Ki and inhibitor type from the concentration of inhibitor for 50% inhibition for Michaelis-Menten enzymes.  Brandt RB, Laux JE, Yates SW.