Question

You have been tasked with isolating two different proteins from a bacterium that grows at 37°C. Part I (a) The first protein you are isolating is found in the organelle of the bacterium that has a pH of 9.4 at 37°C. You need to make up a 1.0 M solution. Which of the following buffer(s) would you choose and why? (2 pts) (Hint: Please note that species concentrations are dependent on the temperature of the solution i e pKa is temperature dependent) Table Buffer Full Chemical Name MW pKa at pKa at (g mol 250C 37C MES 2-(N-Morpholino)ethanesulfonic acid hydrate 195.24 6.10 5.97 Bis-Tris Bis(2-hydroxyethyl methyl methane 209.25 6.50 6.36 302.37 6.76 6.66 PIPES 1,4-P razinediethanesulfonic acid HEPES eth piperazine-1-ethanesulfonic acid 238.30 7.48 7.13 TAPS [(2-Hydroxy-1,lbis methyl)ethyl)amino]-1- 243.28 8.40 8.18 bis(hydroxy propanesulfonic acid CHES 2-(Cyclohexylamino)ethanesulfonic acid 207.29 9.49 9.36 CAPS 3-(Cyclohexylamino)-1-propanesulfonic acid 221.32 10.40 10.02 Here are the structures for the above compounds Bis-Tris MES PIPES HO3S SO3H S-OH xH2O OHHO TAPS HEPES CHES HO SO3H S-OH HO OH CAPS NJ S-OH

Answer 1

1) a) The relationship between pH and pKa of buffer solution is given by Henderson-Hasselbach equation.

pH = pKa + log (HA/A)

For effective buffets, concentrations of HA and A are equal.

So, pH = pKa

pH of the bacterial cell wall is 9.4

Among the given solutions, the pKa of CHES is in close range with the bacterial pH at 37 degrees temperature. Therefore, the best buffer to use at pH 9.4 is CHES buffer.

b) The pKa of given buffer solution at 37 degrees temperature is given below,

10M HCl - 0

10M NaOH - 7

MES sodium salt - 5.97

BIS-TRIS HCl - 6.36

PIPES sodium salt - 6.66

HEPES sodium salt - 7.31

TAPS sodium salt - 7.18

CHES sodium salt - 9.37

pKa of CHES sodium salt and TAPS sodium salt resemble pH of the bacteria. Therefore, these two compounds can be used to make up the pH 9.4 buffer.