Biomedical subjects

W Lohmann

Publications and source records attributed to W Lohmann.

96 records · Page 6Linked to original sources

PubMedDate not supplied

Interaction between spin labels and DPPC vesicles.

1H NMR studies on DPPC vesicles labeled with the spin labels (1,14) or (12,3) have shown that both of the spin labels influence the fatty acid side chains as well as the choline head groups. The spin label (12,3) affects, naturally, the head groups stronger than the spin label (1,14), while the reversed effect can be observed at the side chains. This effect progresses with time after vesicle preparation and is fully developed after about 24 h. Addition of Na-ascorbate, at this time, seems to reverse the effect indicating a stabilizing effect of the vitamin on the membrane. These results could be confirmed by ESR investigations according to which the high-field signal seems to be indicative for changes occurring at the side chains, while the low-field signal seems to reflect modifications of the head groups. Since the spin label (1,14) affects considerably the head groups at temperatures less than 6 degrees C, in which case the spectrum is very similar to that obtained with spin label (12,3) at 24 degrees C, one might conclude that there might be a phase transition in regard to the head groups.

1,2-Dipalmitoylphosphatidylcholine↗

PubMedDate not supplied

Fluorescence studies on lung tumors.

Illumination of unstained 9 microns cryosections of lung tissue with 365 nm results in visible fluorescence light with a maximum intensity at about 460 nm. These fluorescence tomographical studies can be used for detecting carcinoma of the lung. The fluorescence pattern obtained can be matched nicely with histological findings. Since it takes less than 5 min for getting the fluorescence images, the fluorescence tomographical technique might be used in addition to established methods for determining the histology of a biopsy sample.

Adult↗

PubMedDate not supplied

Elastosis and cancer.

Recently we have shown that the autofluorescence within or just outside of a malignant tumor is rather small or large resp. in comparison to healthy tissue when excited at 365 nm. Studies with unfixed, unstained cryosections of skin with melanomas have revealed bulky fiber-like structures with a high fluorescence intensity just outside of a malignant tumor. Using polarized light, the structures could be identified as elastic fibers. This was also confirmed by studies on arterial walls.

Aged↗

PubMedDate not supplied

The diffusion of L(+)-ascorbic acid across DPPC vesicle membranes.

The transmembrane diffusion of L(+)-ascorbic acid has been studied by means of 1H-n.m.r. spectroscopy using small unilamellar DPPC vesicles as a model system. It is shown that the electro-neutral form of L(+)-ascorbic acid diffuses faster across the membranes than the anionic form by about two orders of magnitude. The diffusion is influenced by a molecular interaction between L(+)-ascorbate and the membrane surface and depends also on the fluidity of the membrane. The calculated permeation coefficients of neutral L(+)-ascorbic acid are between 6 x 10(-10) and 3 x 10(-8) cm s-1 (35-52 degrees C).

1,2-Dipalmitoylphosphatidylcholine↗

PubMedDate not supplied

Ascorbate oxidase and its possible involvement in cancer.

The electron spin resonance (ESR) spectrum of erythrocytes of a health male volunteer exhibited 2 min after intravenous administration of 1g of ascorbic acid a considerable increase in spin concentration and an new signal at about g-2.005 which we previously had found to correlate to the semidehydroascorbate (SDA) radical and which is not identical with the O2 radical. Moreover, the vitamin C concentration in erythrocytes and plasma was considerably higher than in comparable samples of other volunteers treated identically. In the latter cases, the ESR spectrum of the erythrocytes was not modified at all. These findings suggest that there must be a substance which reacts with ascorbic acid specifically. It can be assumed that the enzyme ascorbate oxidase plays this decisive role in the ascorbic acid metabolism. For this reason, different amounts of ascorbate oxidase have been added to healthy erythrocytes treated in vitro with ascorbic acid and to tissue samples of lung cancer. As expected, the vitamin C effect as expressed by the appearance of the SDA signal and the increase in spin concentrations could be reversed. It is suggested, therefore, that in special types of cancer, such as acute lymphatic leukemia and lung cancer, the concentration of ascorbate oxidase or of an enzyme acting like it is, primarily, diminished, while in other types it might be enlarged.

Ascorbate Oxidase↗

PubMedDate not supplied

[31P- and 1H-NMR-investigations about the interaction of ATP with Mg2+, Ca2+, and monoamines (author's transl)].

The interaction between aromatic amines and ATP is based upon an electrostatic attraction of the protonated amino groups to the negatively charged phosphate groups of ATP combined with a stacking association between the ring systems. The complexes formed are relatively weak (association constants 4--48 M-1), shortlived (life time smaller than 0.02 s), and mainly 1:1 in stoichiometry preferring the terminal phosphate of ATP as the site of association. The divalent metal ions Mg2+ and Ca2+ bond stronger than the amines (association constants 1500 and 100 M-1, resp.) prefer the beta-phosphate group changing thereby the geometry of the ATP phosphate chain. Thus, they reduce the amine-ATP association in ternary mixtures.

Adenosine Triphosphate↗