B.

A peptide has the following amino acid composition: 

2 Met, 2 Phe, 2 Glu, 1 Arg, 1 Lys, 1 Val, 1 Leu, 1 Gly, 1 Ser 

         Reaction of the intact peptide with dansyl chloride followed by acid hydrolysis creates a       
         derivative of Met. 
 
         A specific cleavage of the intact peptide produces fragments with the following sequences: 
 

Fragment A:    Glu-Gly-Lys-Phe    

                        Fragment B:    Met-Ser-Leu-Arg    
 

Fragment C:    Met-Val-Glu-Phe                   (Questions 6-10) 

 
 
6._____         Which reagent was used for the specific cleavage? 
                        a)         cyanogen bromide  
                        b)         V8 protease 

                        c)         chymotrypsin 

                        d)         trypsin 
 
7._____ 

Which reagent would break only one peptide bond in the intact peptide? 

                        a)         cyanogen bromide  
                        b)         V8 protease 
                        c)         chymotrypsin 
                        

d)         trypsin 

 
8._____         Which amino acid would be released if the intact peptide was treated with a  
                       combination of trypsin and chymotrypsin? 
                        a)         Lys 

                        b)         Phe 

                        c)         Glu 
                        d)         Met 
                          
9._____ 

What information do these result give about the sequence of the peptide? 

a)        The sequence is: Met-Val-Glu-Phe-Glu-Gly-Lys-Phe-Met-Ser-Leu-Arg 

                        b)        The sequence is: Met-Ser-Leu-Arg-Met-Val-Glu-Phe-Glu-Gly-Lys-Phe 
                        c)        The sequence is: Met-Val-Glu-Phe-Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe 

d)        The sequence is: Met-Ser-Leu-Arg-Glu-Gly-Lys-Phe-Met Val-Glu-Phe 
 

10._____ 

 This peptide is one polypeptide chain of a multimeric protein that contains two              

                         non-identical subunits. What problem might be seen when analyzing the primary  
                         structure of the protein if the subunits were not separated? 
 

a) Fluorodinitrobenzene 

might 

react 

with two different amino acids. 

 b) 

Carboxypeptidase might not react with the C-terminals.  

                         c) 

Mercaptoethanol might not reduce disulfide bonds. 

 d) 

Lithium borohydride might cleave peptide bonds randomly. 

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