Wednesday, March 20, 2013

Xanthoproteic Test for Tyrosine and Tryptophan

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Reaction of concentrated nitric acid with some substituted aromatic rings gives a yellow color (Xanthos = yellow in Greek).

Procedure

    Set up test tubes as follows: In one tube put 2 drops of tryptophan solution, in another 2 drops of unknown compound, in another 2 drops of glycine solution, and in another about 5 mg tryosine powder. Then with great care, add 1.0 mL concentrated nitric acid (HNO3) to each test tube. Hold the tubes so that they do not point at you or anyone else.  Heat the tubes gently in a water bath until they boil. Cool the tubes slowly and add the 4% NaOH, drop by drop, until the solutions are alkaline. 

Did any color change take place before the alkali was added? What was the final color of each of the solutions?

Download Free here: Color Reactions of Amino acids

For More: See the Amino acids Video Lectures

See the Practical Video Presentation for better understanding

Wednesday, January 30, 2013

Principles of Gel Electrophoresis

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Electrophoresis: How to Read Results

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Protein Purification with Dialysis Tubing

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Protein Quantification (Bradford Assay)

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Bradford assay is a rapid and accurate method to determine the concentration of protein. The assay is based on the observation that the absorbance maximum for an acidic solution of Coomassie Brilliant Blue G-250 shifts from 465 nm to 595 nm when binding to protein occurs. Both hydrophobic and ionic interactions stabilize the anionic form of the dye, causing a visible color change. Within the linear range of the assay (~5-25 mcg/ml), the more protein present, the more Coomassie binds.

 

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