Insulin, the peptide hormone responsible for controlling blood-glucose levels, i

Question

Insulin, the peptide hormone responsible for controlling blood-glucose levels, is composed of two chains (A and B) that are held together via disulfide bonds. After separating the two chains, you take the larger B chain and subject it to the following analysis: Cleavage of the peptide with altrolysin C (AltC), which cleaves on the N-terminal side of Leu and Phe, gave the following peptides after gel filtration/size-exclusion separation (in order of elution) and MS analysis: Al: LVCGERG A2: FYTPKT A3: FVNQH A4: LCGSH AS: LVEA A6: LY A7: F Cleavage of the peptide with glutamyl peptidase (Glu-C), which cleaves on the C-terminal side of GIu and Cys, gave the following peptides after reverse-phase HPLC separation (in order of elution) and MS analysis: G1: GE G2: GSHLVE G3: FVNQHLC G4: ALYLVC G5: RGFFYTPKT Determine the full sequence of the B chain of insulin from the above data. Does the order of elution of the AltC peptides match what was expected for the gel-filtration/size exclusion column? Why or why not? Draw the G2 peptide in the appropriate protonation state for a pH of 7.5;be sure to show appropriate stereochemistry, provide all pK_AS, and calculate the pi.

Explanation / Answer

(1) sequence of B chain of insulin from the observation will be

N-terminal(F-V-N-Q-H-L-C-G-S-H-L-V-E-A-L-Y-L-V-C-G-E-R-G-F-F-Y-T-P-K-T) C-terminal

this sequence satisfies cleavage from both the enzyme altrolysin and glutamyl peptidase.

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