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Answers to all problems are at the end of this book. Detailed solutions are available in the Student Solutions Manual, Study Guide, and Problems Book. 13. Determining Tyrosine Content of an Unknown Protein A previously unknown protein has been isolated in your laboratory. Others in your lab have determined that the protein sequence contains 172 amine acids. They have also determined that this protein has ne tryptophan and no phenylalanine. You have been asked to determine the possible tyrosine content of this protein. You know from your Study of this chapter that there is a relatively easy way to do this. You prepare a pure 50 mM solution of the protein, and you place it in a sample cell with a 1-em path length, and yen measure the absorbance of this sample at 280 nm in a U V-visible spectrophotometer. The absorbance of the solution is 0.372. Are there tyrosines in this protein? How many? (Hint: You will need to use Beer's law, which is described in any good general chemistry or physical chemistry textbook. You will also find it useful le know that the units of molar absorptivity are M -1 cm -1 .)

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Biochemistry

6th Edition
Reginald H. Garrett + 1 other
Publisher: Cengage Learning
ISBN: 9781305577206

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Chapter
Section
BuyFindarrow_forward

Biochemistry

6th Edition
Reginald H. Garrett + 1 other
Publisher: Cengage Learning
ISBN: 9781305577206
Chapter 4, Problem 13P
Textbook Problem
60 views

Answers to all problems are at the end of this book. Detailed solutions are available in the Student Solutions Manual, Study Guide, and Problems Book.

13. Determining Tyrosine Content of an Unknown Protein A previously unknown protein has been isolated in your laboratory. Others in your lab have determined that the protein sequence contains 172 amine acids. They have also determined that this protein has ne tryptophan and no phenylalanine. You have been asked to determine the possible tyrosine content of this protein. You know from your Study of this chapter that there is a relatively easy way to do this. You prepare a pure 50 mM solution of the protein, and you place it in a sample cell with a 1-em path length, and yen measure the absorbance of this sample at 280 nm in a U V-visible spectrophotometer. The absorbance of the solution is 0.372. Are there tyrosines in this protein? How many? (Hint: You will need to use Beer's law, which is described in any good general chemistry or physical chemistry textbook. You will also find it useful le know that the units of molar absorptivity are M-1cm-1.)

Interpretation Introduction

To propose:

Determine tyrosine content of an unknown protein.

Introduction:

The amount of tyrosine in the protein can be determined using Beer’s law:

A=εlc

Where A is the absorbance, εis the molar absorptivity, l is the path length and c are the absorbing specie’s concentration in solution.

Explanation of Solution

The significant absorbance of the UV light above 250 nm indicates the existence of aromatic amino acids. Because tryptophan and phenylalanine do not exist in the protein, tyrosine must be existing in the protein.

The amount of tyrosine in the protein can be determined using Beer’s law:

A=εlc

Where A is the absorbance, εis the molar absorptivity, l is the path length and c are the absorbing specie’s concentration in solution.

Substituting into the equation for absorbance, molar absorptivity and path-length allows the concentration of tyrosine in solution to be determined. The molar absorptivity of tyrosine at 280 nm is about 1000 M-1cm-1.

              0.372=(1000M1cm1)(1cm)c     0.3721000M1=c3.72×104M=c     0

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