title: The enzyme horseradish peroxidase is less compressible at higher pressures.
abstract: Fluorescence line-narrowing (FLN) spectroscopy at 10 K was used to study the effect of high pressure through the prosthetic group in horseradish peroxidase (HRP), which was Mg-mesoporphyrin (MgMP) replacing the heme of the enzyme. The same measurement was performed on MgMP in a solid-state amorphous organic matrix, dimethyl sulfoxide (DMSO). Series of FLN spectra were registered to determine the (0, 0) band shape through the inhomogeneous distribution function (IDF). In the range of 0-2 GPa a red-shift of the IDF was determined, and yielded the isothermal compressibility of MgMP-HRP as 0.066 GPa(-1), which is significantly smaller than that found earlier as 0.106 GPa(-1) by fine-tuning the pressure in the range up to 1.1 MPa. The vibrational frequencies also shifted with pressure increase, as expected. The compressibility in the DMSO matrix was smaller, 0.042 GPa(-1), both when the pressure was applied at room temperature before cooling to 10 K, or at 10 K. At 200 K or above, the bimodal (0, 0) band shape in DMSO showed a population conversion under pressure that was not observed at or below 150 K. A significant atomic rearrangement was estimated from the volume change, 3.3 +/- 0.7 cm(3)/mol upon conversion. The compressibility in proteins and in amorphous solids seems not to significantly depend on the temperature and in the protein it decreases toward higher pressures.
authors.affiliation: Institute of Biophysics and Radiation Biology, Semmelweis University, Budapest H-1444, Hungary. smeller@puskin.sote.hu
authors.forename: László
authors.initials: L
authors.lastname: Smeller
authors.forename: Judit
authors.initials: J
authors.lastname: Fidy
mesh_terms: D004121:Dimethyl Sulfoxide; D006418:Heme / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000737:chemistry*; D008652:Mesoporphyrins / Q000737:chemistry*; D011312:Pressure; D013050:Spectrometry, Fluorescence / Q000379:methods; D014732:Vibration
chemical_list: D008652:Mesoporphyrins; C039630:magnesium mesoporphyrin; D006418:Heme; D006735:Horseradish Peroxidase; D004121:Dimethyl Sulfoxide