Raman spectroscopy of liver alcohol dehydrogenase

Signature molecular changes in the skeletal muscle of hindlimb unloaded mice

Hind-limb unloaded (HU) mouse is a well-recognized model of muscle atrophy; however, the molecular changes in the skeletal muscle during unloading are poorly characterized. We have used Raman spectroscopy to evaluate the structure and behavior of signature molecules involved in regulating muscle structural and functional health. The Raman spectroscopic analysis of gastrocnemius muscles was compared between 16-18 weeks old HU c57Bl/6J mice and ground-based controls. The spectra showed that the signals for asparagine and glutamine were reduced in HU mice, possibly indicating increased catabolism. The peaks for hydroxyproline and proline were split, pointing towards molecular breakdown and reduced tendon repair. We also report a consistently increased intensity in> 1300 cm-1 range in the Raman spectra along with a shift towards higher frequencies in the HU mice, indicating activation of sarcoplasmic reticulum (SR) stress during HU.

The determination of the pKa of histidine residues in proteins by Raman difference spectroscopy

Sensitive Raman difference spectroscopy was used to monitor the protonation and deprotonation of histidine residues in apo-transferrin. We have shown previously that the behavior of small molecules and/or small molecular groups bound to proteins or other large macromolecules can be studied by Raman difference spectroscopy (Yue, K.T. et al. (1989) J. Raman Spectrosc. 20, 541-545). Using this method, we have measured the Raman difference spectra of human transferrin at different pH values with respect to pH 8.9, titrating its various histidine residues. About 12 +/- 2 of the 19 residues were titrated. The pH difference spectrum of transferrin obtained is very similar to that of histidine in solution, but with clear differences in the 1200-1400 cm-1 region. A titration curve with pKa of 6.08 +/- 0.01 fit the data of histidine in solution and a value of 6.56 +/- 0.02 was found for the average value of the 12 histidine residues inside transferrin. The technique has enough sensitivity at present to monitor a single histidine residue in a 130 kDa molecule and to determine the titration curve of one residue in a 40 kDa protein.