An Fab fragment binds to lysozyme with a dissociation constant of K4 = 10 M. A 1 nM (10 M) solution of lysozyme is treated with increasing concentrations of the Fab fragment. At what concentration of added Fab will half of the lysozyme be bound to the Fab? nM

Need help, please. Answer choices are provided below for drop-down questions. 1. The overall charge of this protein at pH 7 is Drop-down answer choices are [positive, negative, or neutral] 2. In the first dimension of 2-D PAGE, this protein's isoelectric focusing point is  Drop-down answer choices are [between 4 and 6, between 6 and 8, or between 8 and 10] 5.  A mole of the above protein weighs ____ g. For 1 mL of a 3 mM solution of the above protein, you would need to weigh out ____ Drop-down answer choices are [g, mg, mcg, ng, or pg]  (number and unit, at least one non-zero integer to the left of the decimal point, don't round)

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Dear Expert. Thank you for your advice, which is good and helpful. I note that your answer is "when 3 binding sites have been occupied the activity of these receptors is maximum." However, I also note that for a similar question (see below) on α7 nicotinic Acetylcholine Receptor (nAChR) also gives the same answer, ie. at least 3 agonist binding sites should be occupied.  Another Question - "To maximize the activity of an α7 nAChR, how many agonist binding sites should be occupied." I understand that in α7 nAChR, binding to two sites is more effective and binding to three sites is most effective for activation. On the other hand, binding to four or five sites in the nAChRs of chromosome 7 speeds up desensitization more than activation. Therefore, to maximize the activity of an α7 nicotinic Acetylcholine Receptor (nAChR) is also "3 sites". Am I right?