Draw the structure of pentapeptide Trp-Asp-Cys-Lys-Gln that would predominate in aqueous solution at pH=5.5. (Relevant pKa values are 2.2, 3.8, 8.3, 9.6 and 10.5.)
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- Draw the structure of the pentapeptide Gln-Trp-His-Glu-Tyr that would predominate in acqueous solution at pH=10.3. (Relevant pKa values are: 2.2,4.3,6.0,9.8 and 10.1)A tetrapeptide, glutamate-glycine-alanine-lysine, is prepared at at concentration of 1 mM (0.001 M) and is measured in the standard setup (pathlength of 1 cm). What is the approximate absorbance of this peptide at 280 nm? Hint: if the peptide contained a single tryptophan, the answer would be about 10. 10 280 1 0c) A lysine residue in the active site of UstD is involved in forming a covalent Schiff base linkage with the PLP cofactor. In order for this linkage to form, the lysine residue must be in its deprotonated form. Draw the structure of the R group of lysine in this neutral form. What is the ratio of the concentration of this form to that of its conjugate acid form at neutral pH? ( )
- Protein concentration can readily be determined using the Beer-Lambert law: A = e l c where A = absorbance e = molar absorption coefficient (M-1cm-1) l = light path length (cm) c = concentration (M) If the molar absorption coefficient at 280 nm for yeast ADH is 48860 M-1cm-1 and a 10 mL solution of the protein has an absorbance at 280 nm of 0.4 (as measured by a spectrometer with pathlength 1 cm), then what is the concentration of the protein solution (in μM)? i.e. concentration = ______ μM If the molecular weight of the protein is 36849, what is its concentration in mg/mL? i.e. concentration = _______ mg/mL For each part of the question, show your calculations to arrive at your answers.Some of the following four amino acids : alanine, arginine, histidine, aspartic acid would provide a side chain for acid-base catalysis at physiological pH (assume pK of each amino acid is equal to pK value for the free amino acid in solution). Explain for each amino acid how and why each would or would not provide the side chain residue to support acid-base catalysis at physiological pH.The octapeptide gly-cys-met-asn-lys-ala-tyr-gly was hydrolyzed consecutively by CNBr and then trypsin (3 fragments total). The mixture of fragments was buffered at a pH 8.5 and then chromatographed on an anion-exchanger (positive resin) with the same buffer. Draw sequence (abbreviated form) of all fragments at that pH (show charges) and predict elution order.
- you have the following peptide Arg-Ile-Pro-Leu-Asp-Lys-Glu The net charge on this peptide at pH 7.0 is ?. The net charge on this peptide at 1M HCl is ?.Kwon Soon-young was asked by his CHEM 160.1 lab instructor to determine the isoelectric pH of an unknown protein sample which is said to be 20% histidine (pI = 7.59), 25% lysine (pI = 9.74), and 55% arginine (pI = 10.76). He plans to perform isoelectric precipitation in order to determine the IpH of the unknown protein sample. From the three buffer solutions below, at which particular buffer system do you think the unknown protein is most likely to precipitate? Explain your reasoning. BUFFER SYSTEM citrate buffer bicarbonate buffer methylamine-methylammonium chloride buffer pH 3.15 7.41 10.46b) Consider the following experimental results: Total hydrolysis of a nonapeptide gave: Ala,Arg,Glu,Leu,Lys,Met,Phe,Tyr, Val One fragment from CNBr treatment was: Tyr-Leu-Lys One fragment from Chymotrypsin treatment was Arg-Glu-Met-Tyr One fragment from Trypsin treatment was Val-Ala-Phe-Arg ii. The reagent shown below is widely utilized in the sequencing of peptides. Treatment of the nonapeptide you deduced in part i. with this reagent yields a phenylthiohydantoin derivative, compound 1, and an octapeptide. Write a mechanism for the formation of compound 1. N=c=8
- The extinction coefficient or absorptivity (ɛ) of protein A at 340 nm is 6440 M-1 cm-1, whereas protein B does not absorb at 340 nm. What absorbance will be observed when light at 340 nm passes through a 5 mm cuvette containing 10 µM of protein A and 10 µM of protein B? Beer-Lambert-law; A = ɛ x C x1; A = absorbance, C= concentration, 1= pathlength).Given the following pKa data for the individual amino acids, estimate the pI for the tripeptide Thr-Asp-Arg. N-terminal amino group = 9.10 Side chain of aa #1 = Side chain of aa # 2 = 3.86 Side chain of aa # 3 = 12.48 C-terminal carboxyl group = 2.01 PI =b) Consider the following experimental results: Total hydrolysis of a nonapeptide gave: Ala,Arg, Glu,Leu,Lys,Met,Phe,Tyr,Val One fragment from CNBR treatment was: Tyr-Leu-Lys One fragment from Chymotrypsin treatment was Arg-Glu-Met-Tyr One fragment from Trypsin treatment was Val-Ala-Phe-Arg i. Deduce, with suitable explanations, the amino acid sequence of the nonapeptide.