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Biomedical subjects

H Scheer

Publications and source records attributed to H Scheer.

72 records · Page 4Linked to original sources
PubMed1982

Recombination dynamics in bacterial photosynthetic reaction centers.

The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way.

Bacterial Proteins↗
PubMed1980

Steroid delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase in the rat epididymis during development.

delta 4-5 alpha-Reductase activity is apparently regulated by a testicular factor(s) secreted directly into the epididymis, whereas 3 alpha-hydroxysteroid dehydrogenase activity, in this tissue, appears to reflect circulating androgen levels. To test whether the factor(s) regulating delta 4-5 alpha-reductase activity is directly associated with spermatozoa, a developmental study was undertaken to temporally correlate various parameters of the male reproductive tract with enzymatic activities. delta 4-5 alpha-Reductase activity is first detectable at 21 days of age. Activity increases until day 77, after which time enzymatic activity decreases by more than 60%, reaching steady adult values at 105 days. 3 alpha-Hydroxysteroid dehydrogenase activity is detectable as early as 7 days. Levels of this enzyme increase until day 63, after which time constant adult values are maintained until at least 1 yr. Spermatids and/or spermatozoa are first seen in the testes at 42 days, and plateau levels are reached by day 77. Spermatozoa are first seen in the epididymis at 49 days and reach maximal values by 91 days; no significant change occurs thereafter (until 365 days). Increases in seminal vesicle and ventral prostate weights are of a sigmoidal type, paralleling increases in plasma androgens, with the greatest rate of rise between days 35--63. This sigmoidal type of increase in tissue weights and plasma androgens is similar to that seen for epididymal 3 alpha-hydroxysteroid dehydrogenase but markedly different from that found for delta 4-5 alpha-reductase. The importance of delta 4-5 alpha-reductase and 3 alpha-hydroxysteroid dehydrogenase activities in the epididymis before the entry of spermatozoa and the decline in delta 4-5 alpha-reductase activity with age is discussed.

3-Hydroxysteroid Dehydrogenases↗
PubMed1979

Studies on plant bile pigments, VII. Preparation and characterization of phycobiliproteins with chromophores chemically modified by reduction.

The reversible denaturation and reduction with dithionite has been studied for the phycobiliproteins, C-phycocyanin (1) and allophycocyanin (2) from Spirulina platensis, and C-phycoerythrin (4) from Fremyella diplosiphon (both cyanobacteria). By treatment with sodium dithionite, the chromophores are selectively reduced at the central (C-10) methine bridge, producing pigments with bilirubinoid (lambda max = 418 nm from 1 and 2), and vinylpyrroloc (lambda max= 300 nm from 4) chromophores. The extent of reduction is dependent on the state of the protein. The chromophores of denatured biliproteins are completely reduced at 0.5 mM dithionite. In the native pigments, dithionite concentrations up to 0.5 mM lead only to partial reduction, thus forming products containing both reduced and oxidized chromophores (e.g. "phycocyanorubins" from 1 and 2). The reduction is non-statistical with respect to the different chromophores present in 1 and 4, the chromophores absorbing at shorter wavelengths being preferentially reduced. Renaturation of the proteins containing reduced chromophores is accompanied by their reoxidation. This oxidation is complete in the absence of dithionite or at concentrations up to 0.5 mM. At higher dithionite concentrations, the reoxidation is incomplete, and the products are spectroscopically identical to those obtained by reduction of the native pigments at similar concentrations of reductant. The results are interpreted by a model in which the protein is "transparent" to the reducing agent, dithionite. The difference in the extent of reduction of the native and denatured pigments can only be due to thermodynamic (viz. stability) differences in the susceptibility of the chromophores to reduction. Specifically, the (extended) chromophore present in the native pigment is much more difficult to reduce than the chromophore (present in a cyclic conformation) in the denatured pigment. The energetics of the process of refolding both the protein and the chromophores are discussed.

Apoproteins↗
PubMed1979

[Reaction of articular cartilage to subchondral defect filling with autologous cancelous bone, Kiel's bone chips and bone cement].

Equally sized subchondral osseous defects were produced in 30 adult rabbits. The defects were filled with autologous cancellous bone, bone cement, or macerated heterologous cancellous bone. Twelve weeks later those filled with autologous cancellous bone showed consolidation with preservation of the subchondral border line. There were no degenerative changes of the joint's cartilage. Filling with bone cement or heterologous cancellous bone, on the other hand, led to destruction of the joint's cartilage. The defects treated with heterologous cancellous bone had not reached osseous consolidation at that time. These results suggest that effective treatment of subchondral osseous defects can only be achieved by filling with autologous cancellous bone.

Animals↗
PubMed1977

On the classification of penis carcinoma and its 10-year survival.

With respect to the primary tumor there is no difference between the proposal of the UICC and the Heidelberg version for TNM classification of the penis carcinoma. Clinically the Heidelberg scheme seems more practical, but there were no statistical differences between them. With respect to the prognosis for the patient, the size and localization of the primary tumor are of secondary importance. What is important is the degree of tumor spreading in the lymph system. From this point of view, one needs only to differentiate between T1 (tumor restricted to the penis) and T2 (tumor extending the bounds of the penis). On the other hand, size, localization, and degree of infiltration of penis carcinoma do have different therapeutic consequences, so from this point of view the differentiation of the primary tumor from T1 up to T4 should be retained. With respect to the classification of the state of the corresponding lymph system it is our opinion that the UICC proposal is too differentiated and has little meaning. In its stead, the Heidelberg scheme is clear and simple. Any examiner can complete it. With the help of life tables extending beyond 10 years after diagnosis we were able to determine that 5 years is not a sufficiently long time to clsoe a case of penis cancer. Even with proper treatment, the patient may suffer up to 10 years or more from the disease. In patients aged between 50 and 59 years of age the cancer seems to grow faster; in spite of proper and intensive treatment those patients had a clearly limited life expectancy. In patients aged 60-69 and more so in those between 70 and 79 years of age the tumor seemed to grow slowly and often had no effect on the survival rate.

Follow-Up Studies↗
PubMed1977

Studies on plant bile pigments, II[1]. Chemical and photochemical oxygenation of a phytochrome Pr chromophore model pigment to purpurins.

The chemical and photochemical oxygenation of 2,3-dihydrooctaethyl-1,19(21,24H)-bilindione (1), as a model for the chromophores of both phytochrome Pr and phycocyanin, has been studied in neutral and alkaline solution, and in the presence of zinc ions. By comparison with octaethyl-1,19(21,24H)-bilindione (5), the influence of ring A hydrogenation on the reactivity of bilins has been assessed. In the dark, 1 is attacked selectively and rapidly at C-5 yielding "purpurins", while 5 reacts slowly, and is attacked predominantly at C-10. Photooxidation of 5 yields the tripyrrinic "purpurin" 7 only. Photoreactivity of 1 is considerably enhanced, yielding "purpurins" and "violins" rapidly. In spite of UV-vis and mass spectroscopic similarities, the "purpurin" 7 differs from the "purpurins" 6a,b by the loss of ring A. The facile cleavage at the C-5 methine bridge and the spectroscopic properties of "purpurins" are discussed.

Models, Chemical↗
PubMed1977

[Short-term catheterization following electroresection of the prostate and adenomectomy].

The catheter short-term treatment is used in altogether 500 patients in adenectomy as well as in TUR. Apart from the restoration of regular passage the reduction of the infection of the urinary tract is the most important aim of the surgery of the prostate gland. With the help of the short catheter follow-up treatment within the first four weeks after operation the infection of the urinary tract is cured in 87,5% of the cases. The subjective trouble of the patient is further decreased. Prerequisite for the permanent catheter short-term treatment is the exact operation technique combined with most careful haemostasis.

Electrosurgery↗
PubMedDate not supplied

Chemical modification of biliprotein chromophores.

The reaction of biliproteins with sodium dithionite has been studied. The reagent is selective towards the chromophores. In denatured phycocyanin from Spirulina platensis, all three chromophores react to form yellow "phycorubin", whereas only 1/3 of the chromophores react in native phycocyanin in a non-statistical manner. From reversion experiments, it can be shown, that the thermodynamic stability of the chromophores towards reaction with dithionite is increased in the native pigment. Similarly, native phytochrome in its Pr form reacts only partially to a pigment absorbing at both 420 and 660 nm. The same product is formed from native Pfr, indicating both a reversion to Pr and a partial reduction.

Dithionite↗
PubMedDate not supplied

Reconstitution of an allophycocyanin trimer complex containing the C-terminal 21-23 kDa domain of the core-membrane linker polypeptide Lcm.

Allophycocyanin (AP) was isolated from extracts of the cyanobacterium Mastigocladus laminosus. A fraction enriched in AP-associated polypeptides with apparent molecular masses of 21-23 kDa in SDS-PAGE, was isolated on a preparative scale and identified as a homologous mixture of C-terminal fragments of the core-membrane linker polypeptide Lcm. The complex (alpha AP beta AP)3.21-23 kDa was reconstituted and characterized by sucrose density gradient ultracentrifugation, absorption, fluorescence emission and circular dichroism spectroscopy. The 21-23 kDa polypeptides were found to induce spectral changes in AP similar to those induced by the small core linker polypeptide Lc8.9. Possible functions of the complex in phycobilisomes are discussed.

Amino Acid Sequence↗