Biomedical subjects

G Heibel

Publications and source records attributed to G Heibel.

5 recordsLinked to original sources

PubMed1999

UV resonance Raman spectra reveal a structural basis for diminished proton and CO2 binding to alpha,alpha-cross-linked hemoglobin.

UV resonance Raman difference spectra between ligated and deoxyhemoglobin contain tryptophan and tyrosine signals which arise from quaternary H-bonds in the T state, which are broken in the R state. These H-bonds are unaffected by bis(3,5-dibromosalicyl) fumarate cross-linking at the Lys alpha 99 residues, which prevents dissociation of Hb tetramers to dimers. However, when the pH is lowered from 9.0, or when NaCl is added, intensity is diminished for the tyrosine Y8 and tryptophan W3 bands of cross-linked deoxyHb, but not of native deoxyHb. This effect is attributed to weakening of tertiary H-bonds involving Tyr alpha 140 and Trp alpha 14, when the T state salt bridge between Val alpha 1 and Arg alpha 141 is formed via protonation of the terminal amino group and anion binding. The Tyr alpha 140-Val alpha 93 H-bond connects the Arg alpha 141-bearing H helix with the Lys alpha 99-bearing G helix. Weakening of the H-bond reflects a tension between the fumarate linker and the salt-bridge. This tension inhibits protonation of the Val alpha 1 amino terminus, thus accounting for the diminution of both proton [Bohr effect] and CO2 binding in the T state as a result of cross-linking.

Anions↗

PubMed1994

Conformational analysis of mitochondrial and microsomal cytochrome P-450 by resonance Raman spectroscopy.

Mitochondrial and microsomal cytochromes P-450SCC and P-450LM2 in the ferric substrate-free and substrate-bound states were studied by resonance Raman spectroscopy. In the spectra of cytochrome P-450SCC two conformational states (A and B) were detected, each of them constituting an equilibrium between a six-coordinated low-spin and a high-spin form. Both the conformational and the spin equilibria are pH- and temperature-dependent, which is in line with previously published results [Lange, R., Larroque, C., & Anzenbacher, P. (1992) Eur. J. Biochem. 207, 69-73)]. On the basis of well-resolved resonance Raman spectra, measured at different pH and temperatures, these equilibria were analyzed quantitatively. Both low-spin configurations of A and B exhibit different band patterns in the spin state marker band region, indicating differences in the active-site structures. While in the high-spin configuration of state A the heme iron remains weakly bound by a sixth ligand, the high-spin form of state B is five-coordinated. Binding of cholesterol to cytochrome P-450SCC causes a significant population of the high-spin forms, particularly of state A (62%). On the other hand, binding of 22R-hydroxycholesterol to the substrate-free enzyme leaves the overall spin equilibrium largely unchanged, i.e., six-coordinated low spin (76% A and 24% B). In both substrate-bound complexes, interactions between the substrate and the heme lead to small but distinct differences in the resonance Raman spectra of the low-spin form of state A. In contrast to cytochrome P-450SCC, the resonance Raman spectra of microsomal cytochrome P-450LM2 provide no indications for multiple conformers at 22 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗

PubMed1993

Structural changes in cytochrome c upon hydrogen-deuterium exchange.

The resonance Raman spectra of yeast ferri- and ferro-iso-1-cytochrome c dissolved in H2O and D2O are reported. Hydrogen exchange in the protein leads to distinct spectral changes of heme vibrational bands, particularly in the region between 670 and 710 cm-1 and at approximately 443 and approximately 450 cm-1. The latter two bands, which have previously been assigned to porphyrin modes including bending vibrations of the propionate side chains [Hildebrandt, P. (1991) J. Mol. Struct. 242, 379-395], reveal frequency shifts by up to 4 cm-1. These shifts are attributed to structural changes of the propionate groups caused by the energetic differences of the hydrogen and deuterium bonds between these substituents and the adjacent amino acid residues. The frequency shifts of the bands between 670 and 710 cm-1 most likely reflect structural differences of the tetrapyrrole macrocycle itself. Time-dependent experiments revealed that the hydrogen exchange processes associated with the changes in the resonance Raman spectra are complete in less than 15 min. The protons which are involved are those in the interior of the heme pocket as concluded by comparison with the exchange rate constants previously determined by NMR spectroscopy [Mayne, L., Paterson, Y., Cerasoli, D., & Englander, S. W. (1992) Biochemistry 31, 10678-10685]. These protons are part of a hydrogen bonding network including the amide protons of Asn-52, Met-80, and Lys-79, the side chain protons of Asn-52, Tyr-67, Thr-78, Trp-59, and Thr-49, and the water molecules 121 and 166.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome c Group↗

PubMed1992

Fourier transform resonance Raman spectroscopy of phytochrome.

The Pr and Pfr forms of phytochrome in H2O and D2O have been studied by Fourier transform resonance Raman spectroscopy with near-infrared excitation (1064 nm). It is demonstrated that this technique is a powerful method for analyzing the chromophore structures of photosensitive pigments. The high spectral quality allows discussion of vibrational assignments based on an empirical approach using previously published data obtained from model compounds. The reduction in intensity of a high-frequency band assigned to the ring-C/D methine bridge vibration is an indication for the non-coplanarity of the ring D in Pfr. The high intensity of a C-H out-of-plane vibration also supports this hypothesis. In Pr, a broad peak at approximately 1100 cm-1 is assigned to an out-of-plane vibration of a strongly hydrogen-bonded pyrrole C=NH+ group. It is missing in Pfr, suggesting deprotonation of the corresponding ring during the transformation from Pr to Pfr.

Chemical Phenomena↗

PubMed1991

Resonance Raman study of cytochrome aa3 from Sulfolobus acidocaldarius.

The single subunit terminal oxidase of Sulfolobus acidocaldarius, cytochrome aa3, was studied by resonance Raman spectroscopy. Results on the fully oxidized, the fully reduced, and the reduced carbon monoxide complex are reported and compared with those of eucaryotic cytochrome oxidase. It is shown that in both redox states the hemes a and a3 are in the six-coordinated low-spin and six-coordinated high-spin configuration, respectively. The resonance Raman spectra reveal far-reaching similarities of this archaebacterial with mammalian or plant enzymes except for the reduced form of heme a. The formyl substituent of this heme appears above 1640 cm-1, ruling out significant hydrogen bonding interactions which is in sharp contrast to beef heart cytochrome oxidase. In addition, frequency upshifts of the marker bands v4 and v2 are noted indicating differences in the electron density distribution within the molecular orbitals of the porphyrin.

Archaea↗