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Amino Acid

M.W. g/mol

pKa for side chain

Alanine

89.1

Arginine

174.2

12.48

Asparagine

132.1

Aspartate

133.1

3.90

Cysteine

121.1

8.37

Glycine

75.0

Glutamate

147.1

4.07

Glutamine

146.1

Histidine

155.1

6.04

Isoleucine

131.2

Leucine

131.2

Lysine

146.2

10.54

Methionine

149.2

Proline

115.1

Phenylalanine

165.2

Serine

105.1

Threonine

119.1

Tryptophan

204.2

Tyrosine

181.2

10.46

Valine

117.1

Take a look at your pKa table for the amino acids. It turns out that when these side chains are in a protein, they can have very different pKa values. Explain the following observations:

a. In the enzyme medium chain acyl-CoA dehydrogenase (b-oxidation of fatty acids), E376 has a measured pKa ~ 8.0. It is found in a very hydrophobic environment. What could account for it elevated pKa?

b. For the enzyme aconitase (Krebb’s Cycle), a catalytic serine is known to have a pKa ~ 8. What kind of factors could account for this decrease in pKa?

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Lelia Lubowitz
Lelia LubowitzLv2
29 Sep 2019

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