Biomedical subjects

V Krüger

Publications and source records attributed to V Krüger.

5 recordsLinked to original sources

PubMed2002

Wavelet networks for face processing.

Wavelet networks (WNs) were introduced in 1992 as a combination of artificial neural radial basis function (RBF) networks and wavelet decomposition. Since then, however, WNs have received only a little attention. We believe that the potential of WNs has been generally underestimated. WNs have the advantage that the wavelet coefficients are directly related to the image data through the wavelet transform. In addition, the parameters of the wavelets in the WNs are subject to optimization, which results in a direct relation between the represented function and the optimized wavelets, leading to considerable data reduction (thus making subsequent algorithms much more efficient) as well as to wavelets that can be used as an optimized filter bank. In our study we analyze some WN properties and highlight their advantages for object representation purposes. We then present a series of results of experiments in which we used WNs for face tracking. We exploit the efficiency that is due to data reduction for face recognition and face-pose estimation by applying the optimized-filter-bank principle of the WNs.

Journal Article↗

PubMed1994

Heterogeneity in rabbit liver cytochrome P-450 LM2 observed by cation exchange HPLC: partial biochemical characterization of the two major LM2 subfractions.

Cytochrome P450 LM2 (CYPIIB4) from phenobarbital-induced rabbit liver microsomes, purified to only one band in SDS-PAGE, was further resolved in five peaks by cation exchange HPLC. The two major peaks were partially characterized. Both of them have the amino terminal sequence Met-Glu and the same Cys content. They exhibited the same spectral absorption maximum and similar binding constants for 1-benzylimidazole and imidazole. However, binding of benzphetamine was different. One subfraction presented a Michaelis-Menten type binding curve, but the other presents a non-typical one with an additional high affinity binding site. These subfractions of cytochrome P450 LM2 slightly differed in their catalytic activities with benzyloxy- and pentoxyresorufin substrates. On the contrary, no heterogeneity was observed for P450 LM4.

Animals↗

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

Rotation of cytochrome P450SCC (CYP11A1) in proteoliposomes studied by delayed fluorescence depolarization.

The rotational diffusion of cytochrome P450SCC (CYP45011A1) was investigated in proteoliposomes measuring the time-resolved delayed fluorescence anisotropy of diiodofluorescein iodoacetamide covalently and specifically attached to Cys264 of P450SCC. Rotation strongly depends on the lipid composition of the membrane, especially on the cardiolipin content. In proteoliposomes having a lipid composition similar to the inner membrane of bovine adrenal mitochondria P450SCC is rotating uniaxially with a relaxation time phi rot about 53 microseconds and almost no immobile P450 is present. Addition of high KCl concentration has no effect. The results and the absence of any intramembrane particles observed by freeze-fracturing indicate that P450SCC probably exists in the liposomal membrane as oligomer not penetrating the bilayer. It is suggested to bind tightly within the outer monolayer with large parts exposed to the aqueous solution surrounding the membrane.

Adrenal Glands↗

PubMedDate not supplied

Direct visualization of a cardiolipin-dependent cytochrome P450scc-induced vesicle aggregation.

Cytochrome P450scc can be reconstituted successfully into large unilamellar phospholipid vesicles by a combined octylglucoside dialysis/adsorption method. Freeze-fracture electron microscopy was used to analyze the morphology, distribution, and protein topology of the cytochrome P450scc vesicles in dependence on lipid composition. Particles were observed only in close contact to the vesicle surface, probably representing tightly associated cytochrome P450scc at the outer vesicle surface. In cytochrome P450scc vesicles similar in lipid composition to the inner membrane of bovine mitochondria direct evidence by freeze-fracturing was found for a specific cytochrome P450scc-induced aggregation of the vesicles. The vesicle aggregation critically depends on the content of the specific mitochondrial membrane constituent cardiolipin. The aggregation and thus the intervesicular contacts were observed to be inhibited by both addition of anti-cytochrome P450scc IgG and adrenodoxin. Enzymatic reduction of cytochrome P450scc in the liposomal membrane by its electron transfer partners completely indicates an asymmetrical localization in/at the outer side of the bilayer membrane. It is suggested that vesiculation of the inner mitochondrial membrane may be a consequence of the characteristic cardiolipin-dependent cytochrome P450scc membrane topology: the cardiolipin binding, peripheral, non-bilayer-spanning integration as an oligomer in the outer leaflet of the membrane may play a role in the dynamics of formation and dissociation of intramitochondrial vesicles with a functional importance for steroidogenesis.

Adrenodoxin↗