Hi all, So this equation is a part of my graduate biochemistry section in MIT (I am an undergraduate). I have weak math foundations but I am working hard on improving that.

Would you please explain to me how did they exactly substitute Kd in Step 2? Because I can't seem to understand how Kd/A appeared there. (Please be simple, I know it is very easy and straightforward but not to me) Also please refer me to resources to improve my weakness.

Reference https://ocw.mit.edu/courses/biology/7-51-graduate-biochemistry-fall-2001/lecture-notes/fa01lec07.pdf (Lecture itself is on Edx)

Knowing Kd = (A) * (B) / (AB)

fraction B bound =

Step 1 ( Divide by AB) [AB] / [B] [AB]

= 1 / [B]/[AB] 1

Step 2 substitute with Kd

= 1 / Kd/[A] 1

Step 3 multiply by A

= [A] / Kd [A]

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Thank youu and sorry for the ugly representation for the equation, reddit isn't helping me with the format( Or I don't know how to properly do it, but it is in the reference link).