Net_charge

# Net_charge - Calculation of Net Charge of a protein at a...

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Calculation of Net Charge of a protein at a given pH (Using the Henderson-Hasselbalch equation) pH = pK a + log [A - ] [HA] Solve for D (pK = 4.5) at a pH 4.9 4.9 =4.5 + log [A-]/[HA] 10 4.9-4.5 =log [A - ]/[HA] 10 0.4 = [A - ]/[HA] 2.512=[A - ]/[HA] remember that this a ratio over 1. The easiest way to calculate this is use “parts” of the total solution : [A - ] has 2.512 “parts” [HA] has 1 “part” The total “parts” is 3.512 Calculate the concentration of the charged elements as a percentage of the total : average charged (A - ) = 2.512/3.512 = 0.71 Remember that your base equation is going to look a little different: pH=pKa + log [B]/[BH + ] Solve in the same way, finding “parts’ for [BH + ] To calculate pI To calculate the net charge of a protein at a given pH 1. List ionizable residues 2. Make assumptions: If pKa ≤ 2 units away from pH, charge can be assigned (as 1, 0, -1) without calculation. 3. Use H-H equation to calculate % ionization (Remember difference between H + acceptor and donator) 4. Multiply charge (z

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Net_charge - Calculation of Net Charge of a protein at a...

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