Protein kinases like platelet-derived growth factor have the ability to phosphorylate tyrosine residues of other proteins and play prominent roles in the regulation of normal growth as well as tumor growth. We will investigate how Src kinase binds to some synthesized peptide inhibitors. We propose to investigate this binding process by tracking spectroscopic changes that result from inhibtor-Src kinase interaction. Initially, we will identify marker bands that would be used as indicators of binding by using some amino acids and their derivatives that can be found on the inhibitor. Good candidates are the phosphate group modes on phosphotyrosine and the ring modes of pentafluorophenylalanine. Using fluorescence spectroscopy, we determined that phosphotyrosine was blue-shifted compared to tyrosine. Tyrosine had a �max at 275 nm. Phosphotyrosine had a �max at 267 nm. Fluorescence can not be used to determine marker bands in pentafluorophenylalanine. The marker bands found using FTIR for pentafluorophenylalanine are at 960, 1527 and 1510 cm-1. Using Gaussian 03 ab initio calculations, we were able to verify that the bands correspond to the C-F bonds on the aromatic ring. The marker band found for phosphotyrosine was at 930 cm-1. Again using ab initio calculations, we were able to verify that this band belongs to the phosphate group on phosphotyrosine. We observed a correlation between our experimental results and our theoretical results. Now, we will investigate what happens to these identified marker bands; (a) when the amino acids are incorporated into the peptide chain, and (b) when these synthesized peptides interact with Src kinase. In the end we expect to gain a better understanding of what happens, at the molecular level, during binding. This knowledge will eventually be used to help us obtain insights into how Src kinase works and perhaps device ways of regulating the enzyme.