Consider the peptide:
NH2-GAPAGPAGTGKTETTKDLAKSMALLCWFNCS-COOH
Table I. pK values of some amino acids
amino acid pK of side chain or terminal group Alanine (Ala or A) uncharged Arginine (Arg or R) 12.5 Asparagine (Asn or N) uncharged Aspartic acid (Asp or D) 3.9 Cysteine (Cys or C) 8.3 Glutamic acid (Glu or E) 4.3 Glycine (Gly or G) uncharged Histidine (His or H) 6.0 Leucine (Leu or L) uncharged Lysine (Lys or K) 10.8 Phenylalanine (Phe or F) uncharged Serine (Ser or S) uncharged Tryptophan (Trp or W) uncharged Tyrosine (Tyr or Y) 10.9 Valine (Val or V) uncharged peptide N terminus 7.8 peptide C terminus 3.6
Using Table I above, determine the net charge of the peptide at pH9.
(the answer is not -1 or 1)
Consider the peptide:
NH2-GAPAGPAGTGKTETTKDLAKSMALLCWFNCS-COOH
Table I. pK values of some amino acids
| amino acid | pK of side chain or terminal group |
|---|---|
| Alanine (Ala or A) | uncharged |
| Arginine (Arg or R) | 12.5 |
| Asparagine (Asn or N) | uncharged |
| Aspartic acid (Asp or D) | 3.9 |
| Cysteine (Cys or C) | 8.3 |
| Glutamic acid (Glu or E) | 4.3 |
| Glycine (Gly or G) | uncharged |
| Histidine (His or H) | 6.0 |
| Leucine (Leu or L) | uncharged |
| Lysine (Lys or K) | 10.8 |
| Phenylalanine (Phe or F) | uncharged |
| Serine (Ser or S) | uncharged |
| Tryptophan (Trp or W) | uncharged |
| Tyrosine (Tyr or Y) | 10.9 |
| Valine (Val or V) | uncharged |
| peptide N terminus | 7.8 |
| peptide C terminus | 3.6 |
Using Table I above, determine the net charge of the peptide at pH9.
(the answer is not -1 or 1)
Related textbook solutions
Related questions
For the following strand of DNA, use the table below to provide: bases for the complementary mRNA and the associated amino acids. What do you notice about the genetic code for proline in the peptide? How would the loss of the first G or switching that G to a T affect the structure and function of this protein?
DNA: GGC CTA CAA GCC GGA ACA GTT ACC GCG TAA CGA
RNA: ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ???
Amino Acid:??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ???
(3 Letters)
Genetic Code Table (mRNA)
| 1st position (5' end) | 2nd position (middle) | 3rd position (3' end) | |||
| U | C | A | G | ||
| U | Phe F Phe F Leu L Leu L | Ser S Ser S Ser S Ser S | Tyr Y Tyr Y STOP STOP | Cys C Cys C STOP Trp W | U C A G |
| C | Leu L Leu L Leu L Leu L | Pro P Pro P Pro P Pro P | His H His H Gln Q Gln Q | Arg R Arg R Arg R Arg R | U C A G |
| A | Ile I Ile I Ile I Met M | Thr T Thr T Thr T Thr T | Asn N Asn N Lys K Lys K | Ser S Ser S Arg R Arg R | U C A G |
| G | Val V Val V Val V Val V | Ala A Ala A Ala A Ala A | Asp D Asp D Glu E Glu E | Gly G Gly G Gly G Gly G | U C A G |
| 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 (Krebbâs Cycle), a catalytic serine is known to have a pKa ~ 8. What kind of factors could account for this decrease in pKa?
