Protein Purification : Practice Problems

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Protein Purification: General Biochemistry Questions

• An enzyme (MW 24 kDa, pI 5.5) is contaminated with two other proteins, one with a similar molecular mass and a pI of 7.0 while the other has a molecular mass of 100 kDa and a pI of 5.4. Suggest a procedure to purify the contaminated enzyme. 

• A mixture of lysine, glycine, alanine, isoleucine and glutamic acid are separated by ionic exchange chromatography. What is the order of elution of these amino acids if you use gradient buffer system from pH 10 to pH 2: 
a) with a cation exchange resin?
b) with an anion exchange resin? 

Which column would give the best separation? 

• Which is the best UV wavelength that can be used to detect Aromatic amino acids?

a) 220nm
b) 214nm
c) 280nm
d) 205nm

• What is the net charge (+, 0, -) of the amino acids glycine, serine, aspartic acid, glutamine and arginine at: 

a) pH 2.01

b) pH 3.96 

c) pH 5.68 

d) pH 10.76

• We load a DEAE-cellulose column adjusted to a pH of 6.5 with the following mixture of proteins: ovalbumin (pI = 4.6), urease (pI = 5.0), and myoglobin (pI = 7.0). The proteins are eluted first with a buffer of weak ionic strength at a pH of 6.5, and then the same buffer containing increasing amounts of sodium chloride is used to elute the proteins. What order are the proteins eluted? 

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