Effects of polar charged amino acids on quantum yield of Tyrosine and Tryptophan

Abstract

Amino acid fluorescence is of particular interest due to its use in determining structural relationships of proteins. The current research is focused on understanding the role of donating amino acid groups on the natural fluorescence of aromatic amino acids, tyrosine and tryptophan. To do this the percentage volume by volume of two polar amino acids, aspartic acid, and glutamic acid within the vicinity of aromatic amino acids, tyrosine and tryptophan were varied. The fluorescence was then measured, and the quantum yields calculated. The results show that the addition of 3.34 mM (25% vol/vol addition) of either glutamic acid or aspartic acid to a 10.28 mM solution of Tryptophan increased the quantum yield by about the same amount. This increase was significantly greater if both concentrations of glutamic acid and aspartic acid (50% v/v) were combined at the same time. However, using a 25% vol/vol addition of glutamic acid and aspartic acid to tyrosine did not have the same effect on the quantum of tyrosine, with aspartic acid showing a quantum yield increase of 0.178 compared to 0.143 shown by glutamic acid. In addition, the combined effect of both amino acids was not greater. The results indicate that tyrosine emits photons in the presence of either glutamic acid or aspartic acid disproportionally while tryptophan does not. On the other hand, the combined effect of both aspartic acid and glutamic acid causes greater photon emission in tryptophan. These results if proven would suggest that photon emission effect of aromatic aminos is greatly influenced by the concentration and types of amino acids within the vicinity of emitting amino acids.