Question

This last set of questions builds on the previous series. You have purified an enzyme catalyzing a disulfide exchange on keratin polypeptides and is called KDI (keratin disulfide isomerase). In order to simplify the protein sequencing, you try to split the protein into large fragments first. You can do this by adding a little bit of subtilisin, a protease that is nonspecific but will cleave unstructured regions. When you do this, you get 2 polypeptides: -8 kDa &-33 kDa. The smaller one binds to keratin but has no enzymatic activity, while the large one has enzymatic activity but no binding domain" affinity for keratin. You call the small fragment KDI-KBD for "KDI keratin You try to dansylate KDI-KBD by treatment with dansyl chloride.. You perform amino acid hydrolysis, and the only fluorescent products are 4 equivalents of monodansyl-Lys and 1 equivalent of dansyl- Asn. Which amino acid is found at the N-terminus of KDI-KBD? Lysine Aspartate O Asparagine

Answer 1

Lysine 2 Lysine has an alpha carbon To answer this question, you need to take two things in consideration: H2N OH 1 The lysine has a amine group at the end The N-terminus of any peptide has a amine group NH2 Aspartate 2 The amine group has to be linked with an alpha carbon HO. - + NH3+ 1 In aspartate, the amine group is not at the end, It is in the middle Asparagine The amine group is linked with a C=O group ТОН The asparagine has a amine group at the end So, your answer would be: Lysine