1 November 1990 Ultraviolet resonance Raman and fluorescence studies of growth hormones
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Ultraviolet resonance Raman and fluorescence spectroscopy have been used to study acid-induced structural alterations in growth hormones from three species. Resonance Raman data for porcine (pGH), bovine (bGH) and human (hGH) growth hormones using 222 am laser excitation show strong enhancement of aromatic residues (phenylalanine (Phe), tryptophan (Trp) and tyrosine (Tyr)). Proline (Pro) vibrations are also enhanced. Protein amide backbone and non-aromatic amino acid vibrations are only enhanced slightly, thus they contribute little to electronic absorption at 222 nm. Resonance Raman results indicate that Pro is present in both cis and trans configurations over the pH 8 to 2 range. Vibrational intensities due to the single Trp (observed at 756 and 1557 cm1) increase dramatically when bGH or pGH is partially unfolded in acid. Trp vibrational intensities for hGH change little at acidic pH, and are comparable to the intensities for partially unfolded bGH and pGH. Fluorescence quantum yields and lifetimes from the single Trp in bGH and pGH increase at low pH in a similar manner to the Trp vibrational intensity increase, while the bGH quantum yields and lifetimes do not change at low pH. Since fluorescence intensity changes for bGH as a function of pH appear indistinguishable from the resonance Raman intensity changes, Trp Raman and fluorescence properties are probably influenced by the same molecular interactions. A pK. of 3.7 for the resonance Raman and fluorescence spectral changes indicates that acidic groups (aspartic or glutamic acids) are involved in the structural alterations. The possible roles of disulfide bridges, lysines, and histidines in decreasing Trp vibrational and fluorescence intensities in native bGH and pGH are examined.
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Thomas J. Thamann, Thomas J. Thamann, Henry A. Havel, Henry A. Havel, E. W. Kauffman, E. W. Kauffman, Paul A. Elzinga, Paul A. Elzinga, "Ultraviolet resonance Raman and fluorescence studies of growth hormones", Proc. SPIE 1336, Raman and Luminescence Spectroscopies in Technology II, (1 November 1990); doi: 10.1117/12.22911; https://doi.org/10.1117/12.22911

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